I understand that after you upgraded the processor, the system stop booting up from a warm boot.
I will like you to test the processor by using the Intel® Processor Diagnostic Tool to check if it is over heating and causing stability problems.
A power supply problem can also cause this behavior, trying a different power supply may help you troubleshoot the problem.
I should first write that I got the used E8500 processor off of eBay so I have no idea of its use history. The seller seemed legit though.
I ran the Intel Processor diagnostic tool and it passed fine. Even after the system has been on awhile it reports a processor temperature of 62 degrees C below max. I also ran a program called Core Temp and that reports Core 0 running at 36c and Core 1 at 36c. I have a huge Zalman HSF on the processor so I'm pretty sure the cooling is ok.
One thing I noticed in the BIOS is under hardware monitoring the Processor Thermal Margin is stuck at 20.00c. The number never changes. The MB temp is around 37c, ICH is 78c, and MCH is 66c.
I don't have another power supply but just not sure that's the problem. It's a quality Seasonic 12 and has always worked fine.
One thing I might try is removing and installing again the processor. I might even clean the underside with alcohol just to make sure there's nothing preventing a good contact between the socket pins and the pads on the processor.
Just seems strange that even the reset switch won't force the motherboard to reboot when I attempt a restart and the system is just hung, no video, no POST.
Well I ended up destroying my beloved DP35DP motherboard last night :-( I bougth a really nice Zalman fan that attaches vertically on the processor. The thing about this new HSF is it has a 4-pin plug so I had to plug directly on the motherboard where the fan was running and full RPMs, very annoying and totally unacceptable. Also pulled the E8500 processor, made sure the socket was perfect which it was, the processor was totally clean on the underside also, so put that back in.
Went into the BIOS, tried changing some settings for fan control which made no difference in behavior. The board still won't warm boot or even boot if a change in the BIOS was made, the only way to get the thing to reboot is to cycle the power. Also was getting some OS instability. So then I made what turned out to be a really big mistake, I made a change in the memory timings in the BIOS which matched the markings on the installed memory, thinking that might make the board start behaving. WRONG!
Now the board won't even POST. All it does is give three beeps indicating a memory problem. I tried everything, pulled the jumper, tried recovery, pulled the cmos battery and power cord waiting hours, pushed the power button hoping to bleed off any charge and wipe out the cmos, nothing I tried worked. The board will not post, all it does is beep beep beep :-(
As an epilogue, I removed the E8500 that seemed to cause all these problems, placed it in a Gigabyte mothrboard with a P45 chipset, and the thing works perfectly, totally rock solid system, using it right now, passes the intel diagnostics program, the E8500 was never the problem. The DP35DP with the latest BIOS or maybe any BIOS and hardware build, cannot support the E8500 core2duo.......