I had an idea when I read this, but this is just a theory. Maybe the power supply is barely meeting the requirements for the devices connected to your computer. When the Ethernet cable is plugged in, the power being drawn when you boot is higher than when the cable is not plugged in. That would also explain why the computer shuts all the way down when you only choose a restart.
IF the above is the cause, then the fix would be to get a higher rated power supply. Like, I said, this is just a theory. Maybe someone else has a better idea.
Clever thought, Mark. I have a 400W power supply and very few devices. However, to test your theory I disconnected the power and data cables from everything non-essential (e.g CD, floppy, disconnected the speakers) and attempted start-up. The problem was still there. If I push the power-on button with the ethernet cable connected I get no response. If I disconnect the ethernet cable (either at the computer or the router) it powers up normally. I can connect the cable the instant after power-up starts, even before BIOS kicks in, and it continues to boot normally. Is there a setting in BIOS that could be the culprit? Another thought is a grounding problem.
In doing more diagnostics I found the following:
If I leave my Ethernet cable plugged in during shutdown, then the only way I can start my computer is to (1) unplug the Ethernet cable, (2) unplug the power cord connected to the power supply, (3) plug the power cord back in, (4) push the on button on the front of the machine, and finally (5) plug the Ethernet cable back in as the computer boots up. Everything then works normally after the computer boots up. If I don't unplug and re-plug the power cord no power is fed to the computer when the on button is pushed. The on-off switch on the power supply doesn't help. The computer won't start if the power switch is toggled. I have to pull out the plug and then plug it back in.
If I unplug the Ethernet cable before shutdown, then the computer starts without cycling the power cord and everything is normal after I plug in the Ethernet cable during boot-up.
This behavior is puzzling. I did a Google search and found nothing related. I feel like the Lone Ranger!! Could a motherboard grounding problem cause this weird behavior?
The steps you listed got me to thinking about another possibility. What if there was a grounding problem in the AC power to your computer and the return or ground circuit followed your Ethernet cable? A bad surge protector or a loose wire behind the AC wall plate or at the circuit breaker box could cause faults in your power.
Of course, the circuit problem could be in your case caused by a wire that is broken or not making good contact or some component shorted or open on your motherboard or elsewhere inside your computer. I guess this type of fault could still end up being something inside the power supply too.
I think you are on the right track when you question things like a ground. You might want to rule out external circuit problems by bypassing any power strip or surge protector that you plug into. If that does not work, then you could try moving your computer to a room that is on a different circuit. Even the power cord from the outlet to your computer could be at fault.
Of course, none of these things will help if the problem is inside of your computer, but you will have ruled out some external causes.
Another great idea, Mark.
I moved the computer to another area of my house and connected the power directly to the wall outlet. That didn't help. It still wouldn't start with the ethernet cable connected. I then tried connecting the cable directly from the cable modem, bypassing the router. No help.
Next, I started to look for grounding problems. I disconnected all cables (reset, HDD light, power sw, USB panel) coming from the case to the board. I tried to start the computer by shorting the two power pins with a screw driver. Same symptoms occured. As long as the ethernet cable was attached it would not start. If I disconnected the ethernet cable, I was able to start the computer.
Finally, I removed the motherboard from the case and sat it on a phone book. I still had the power supply and hard drive connected along with the keyboard, mouse, and video. Same symptoms occurred. I could not start up with the ethernet cable connected but was able to do a start-up with the ethernet cable disconnected from the NIC.
At this point I decided that the only logical diagnosis was that the motherboard itself has a fault of some sort. I got a DMA from INTEL and returned the board for replacement. Hopefully, a new board will fix the problem.
Thanks for your help.
I am looking forward to hearing if the board replacement resolves the issue.
I received my new DG965OT motherboard from Intel. I installed it without problems. I held my breath and turned on the power. At this point I did not have my Network Interface Card installed and did not have an ethernet cable connected to the computer. It started to boot, got past POST, and then spontaneously shut off. I knew what to do! I went into BIOS and disabled on-board LAN. The computer then booted properly. I then installed my NIC and connected the ethernet cable to it. The computer would not start. When I pushed the power button, nothing happened. I disconnected the ethernet cable and it started normally. During bootup, I attached the ethernet cable and all was well. I was connected to the internet via my router and everything worked perfectly. I then shut down. I pushed the power button. No response. I pulled out the ethernet cable and pushed the on button. No response. I then pulled the power cable from the power supply and reattached it. I pushed the on button and the computer started normally. I again plugged in the ethernet cable during bootup and all was well.
This is the same quirky behavior I observed with my old motherboard. I decided to switch the power cord for a new one. Same problem. I switched my mouse and keyboard for new ones. Same problem.
I AM STUMPED!
I don't have a short problem with the case. I ran the computer with the motherboard completely out of the case and sitting on a phone book. The only thing connected to the motherboard was the keyboard, mouse, power supply, monitor, and hard drive. The same problem occurred.
I tried moving the computer to a different power source. I plugged it into the wall, bypassing my power strip. Same problem.
My thinking at this time is that there can only be two sources for the problem: BIOS settings or the power supply. It is very odd that I have to disable on-board LAN to get the machine to power up. What other BIOS settings could be interfering with on-board LAN?
A simple solution is to never turn off the computer. It works fine once it boots up. However, it would be cool if I could solve this problem. Any input would be welcome. Thanks in advance.
I am not surprised that nobody came up with any ideas for bios settings. Have you tried replacing the Power Supply or found any other solution?
Mark -- Thanks for the input. I decided to just live with it. As long as I keep the computer on it works fine. It reboots. The only problem is that I have to cycle the power and ethernet cables if a total shut-down occurs. This isn't that big of a deal. I am still suspicious that this is caused by conflicts in my BIOS settings.
Fascinating. Just found this thread whilst googling the very same problem. My symptoms are identical ie. computer ran for years with no problems until a few weeks ago when it stopped powering up unless I unplugged the ethernet cable. (only sometimes though, now and again, it's fine).
Mine is an Abit KN8 motherboard with AMD Athlon 64 4000+ (socket 939) by the way so it's not just an Intel problem.
May be a coincidence but I encountered the problem shortly after some nasty malware/virus problems (sorted now) so I did wonder if it was a BIOS or software issue.
Sorry I can't solve your problem (I too am just "living with it") but I thought you might at least like to know that you're not alone out there!
Thanks for posting, Bob. I wish we could solve this problem. I too am just living with it. I decided to not turn my computer off at the end of the day. I have no problems at all when I do this. I can do a restart without problems. The only issue is that when I shut down I have to disconnect both the power cable from the power supply and the ethernet cable from its slot. I then have to reinsert the power cable and turn the computer on. While it is booting up or after it has booted completely up, I plug in the ethernet cable and the computer works fine. If I try to start the computer without disconnecting the two cables, then nothing happens when I push the on switch. It doesn't power up. Also, I can't just turn off the power switch on the power supply and then start it up. I have to physically remove the cable from the power supply or it won't start.
I have tried everything I can think of except replacing the power supply. I am convinced the problem is either in the power supply or in the BIOS settings. I have an intel motherboard and intel processor. Since your computer is very different, I am now concluding that the problem is something about the power supply.
Thanks. Alas, I'm having a less reliable time. When I posted the last comment the "remove the ethernet cable" method seemed to work perfectly. Then, all of a sudden I got the same problem again even with the ethernet cable out ie. the PC would start for a split second (fans starting up" before cutting out. Only after removing everything (Mouse, keyboard, graphics card etc) did it start and then only after I laid the PC on its side and opened it up to have a look inside.
I remembered the suggestion about maybe the PSU only just coping with the load it was under so tried disconnecting my 2nd DVD drive last night (seldom use it since it's just player not a Writer). This morning, despite the power cable being being plugged in all night, the PC started up first time. I'll keep an eye on it and post an update if I continue to have success (don't want to re-start ijust now, in case it doesn't come on again!)
We have had similar issues at my workplace, on at least 5 PCs running the DG965OT mobo. Several users have reported that they were prompted to reset after installing updates, and Windows would not load after reboot. Disabling NIC in BIOS resolves startup issue, and these users are now running standalone NICs. I'd attempted to remove updates on one of the PCs one-by-one, in case one of these was the culprit, in which case it could be refused on our WSUS server. However, after removing all of the updates that had been applied before the no-load condition, the symptom remained. This condition has occured in all versions of Windows we use. Most of the PCs are running XP, but it has happened on a Vista machine and my own PC, which is running the 7 RTM edition.
So far I have not found what I consider to be an acceptable solution. Installing standalone NICs gets the users back up and running, but the situation is still in the back of my mind, nagging.
edit: one update was not removed while trying to diagnose: Windows Genuine Advantage (or an update to that component), as Microsoft makes this one a little harder to get rid of.
Any chance you are using a POE Switch/Router?
Have you tried using a different CAT5 Cable?
Just some thoughts?