Today I've tried to install a new CPU, i7 870, to my DH55TC motherboard, which had an i5 CPU and worked perfectly.
I've encountered alot of problems and I've decided to write about them to help others that encounter the same problems as I did.
After I finished installing the i7 the first time, the board did POST (1 beep), and immediately after that it followed with 2 beeps and a pause (which indicates a video error).
I've tried removing the graphic card and booting up but it did not work (The reason, as I later discovered was because the i7-870 does not support the onboard graphic card, and must have an external card installed - as described here: DH55TC with no graphics card installed)
Of course I've then tried removing the RAM and doing combos with it, but nothing worked. I've decided this might be because the motherboard's firmware was not upgraded, and does not support this CPU.
So I tried to bring back the i5 CPU, and at that point nothing really worked. The computer did power cycles with no beeping and nothing worked. Without RAM there were the expected 3 beeps, but any combination with RAM caused the power cycle. Also removing the battery or any other "magical" thing did not help.
At this point I thought I might've damaged the CPU or the motherboard, I did not see any bent pins, and I felt I was pretty careful - but the fact was that the old CPU did not work either.
I wanted to take the computer to a shop to cross check the motherboard and CPUs, but unfortunately NO ONE has an LGA1156 anymore, and I could not find a shop that can test my system.
After I discovered the post about the i7 and the onboard video card issue, I realized that this was the problem I've faced with at the beginning! So this was not a firmware issue, and I've decided to install the i7 AGAIN.
But now, same as the i5, I couldn't hear any beeps, and the computer would not boot at all.. (there were no power cycles though)
I was about to give up, because I thought that this was probably a faulty CPU and I might've damaged the motherboard.
But I still thought about the firmware update and I've decided to look that up. I read here: http://www.tomshardware.com/answers/id-1673693/dh55tc-post-beep.html that it's possible to do a firmware update even if the BIOS is corrupt), so I thought I should try that!
When I read how to upgrade the firmware I realized something awful! At some prior attempt with all this messing around THE CONFIGURATION JUMPER which is used to recover the BIOS was accidentally disconnected from the board! (This is probably because of the graphic card, GeForce GTX 470 which is hideously big, and reaches all the way to the end of the motherboard, covering up 2 SATA ports)
This realization made me understand that all the "no boot" faults were actually caused because the motherboard was in RECOVERY MODE.
The motherboard's manual does not say anything about "no beep = recovery mode" (I think this should be in the troubleshooting section!), and no one suggested or mentioned that it's worth checking the jumper settings!
After setting the jumper back to NORMAL MODE, it fixed the issue - the i7 booted up with the external GeForce - and all peace was restored.
I was very frustrated that all of the computer shops, and the forums on the internet, did not suggest this simple cause to the "no post beep syndrom" - So I thought I should write this post to help anyone else that will encounter these problems. CHECK YOUR JUMPER SETTINGS...
It was long day.