I've got a system that's been causing me a lot of trouble over the last few months. Below is a somewhat lengthy saga of my experience with it but it should hopefully provide some thorough problem history. I've provided a TL;DR at the end to provide some summary.
A while ago, the machine started having trouble booting up. I would hit the power switch in the morning, and come back a few minutes later to a blank screen (no input to the monitor). Rebooting didn't help, so I tried plugging directly into the VGA output of the motherboard instead of the DVI output of the GPU. While I didn't get any output from the motherboard, I eventually found that plugging something in to the VGA out would cause the system to boot up.
For a while, I thus ran the system by having a dummy vga cable (that led nowhere) plugged into the motherboard and the actual monitor input plugged into the GPU, which for some reason let the system boot up.
After a while, this dummy cable method stopped working, but I found that by fiddling around in the back a bit (plugging/unplugging the vga and dvi cables) I could eventually get the system to boot.
On several occasions I tried just "waiting it out" but this was never successful, the computer required some sort of interaction to boot and just letting it sit there for a long time did not work.
Another thing to note is that once the system gets past the boot, it is perfectly fine. Soft-resets (doing a "restart" through Windows) also seem to always work, but I haven't performed enough of them to say it always works.
Eventually, I decided that the machine wasn't worth the effort and ceased trying to boot it. Recently, however, I had a bit more time on my hands and wanted to see if I could diagnose and fix the problem.
I started by examining the computer during the "won't boot" phase, after I had pressed the power button but with still no input to the monitor. All the case fans/lights spin up to full blast, and when I get close to it a notice a distinct pulsing sound. The indicator light in the ethernet port also flashes in sync with this pulse. I tried to find out what the source of the pulse was (I suspected the hard drive) so I opened up the case and put my hand on the chassis near the hard drive to see if I could feel the pulse directly there.
Instead, the system suddenly booted up. I repeated this experiment a couple of times and it seemed to me like my direct contact with metal in the case was allowing the system to boot. I suspected that there was some sort of short which I was solving by grounding the machine.
For a while this technique seemed to work but it too decreased in effectiveness over time.
At this point, I decided to finally do some hardware swapping to see if I could isolate the problem. Based on the shorting issue, I figured it was probably related to the power supply. I wasn't too happy with this as it was a fairly new and costly PSU (Silverstone Strider Plus ST50F-P 500W). However, I swapped the PSU out entirely for a slightly older one I had on hand and the issue shortly returned.
I was also a little bit suspicious of the front panel since the issue seemed to be boot related, and the case is by far the cheapest component of the system. I tried unplugging all the front panel plugs and just using a spare power switch from an older computer, but the issue still persisted.
The issue seemed to be very graphic related so I then assumed it might be graphics card related. I tried two other graphics cards, though (one with auxiliary PCIe power and an older one with auxiliary molex) and with both cards the problem still persisted (I'm using the older card now because I'm less concerned if it gets fried).
I've also tried booting without the hard drives and other peripherals but to no avail. So far, I think the only time I had a degree of success was with the GPU removed entirely, but I need to test that a bit further.
More recently, on a couple of occasions the machine has simply shut down a few seconds after boot. After this occurs, the green light on the motherboard remains lit but I have to unplug the PSU entirely and wait for the light to turn off before plugging it in again or the machine will not respond at all to pressing the power switch. After a couple of tries with this, and some plugging/unplugging of the rear VGA and DVI cables, I am able to get the machine to boot.
I also tried resetting the CMOS and flashing the BIOS to the latest version - neither of which helped.
So at this point, I feel like I've narrowed down the problem to either the CPU, the Motherboard, or the RAM. I have yet to try booting with some of the RAM removed because the issue seems so separate, but to be thorough this test is next on my list (after more trying without a GPU). There are 4 sticks of RAM in the system, DDR2, 2x2GB and 2x1GB (all Corsair).
Here is a detailed spec breakdown:
Potential Problem Parts:
ASUS M4A785-M (AM2)
AMD Athlon II X4 635
6.00 GB Dual-Channel DDR2 @ 266MHz
XFX GeForce 250 GTS
Radeon x1950 XT
XFX GeForce 680 XT
Power Supplies Tried:
Silvestone Strider Plus ST50F-P 500W
Ultra ULT-500P 500W
Peripherals: 195GB Western Digital WDC WD2000JS (SATA)
So, does anyone have any thoughts on this issue? I'd like to be able to narrow it down to the Motherboard so I can seek some sort of warranty repair or replacement (the board is only about 1.5 years old).
Does it seem likely/worthwhile to check each of the RAM sticks? Is there anything I should be looking out for, or anything that I should try? Does the issue sound like its related to any specific part?
TL;DR: Computer boot up issues, seems to be related to plugging a vga cable into the motherboard and some sort of shorting problem, but is power-supply and gpu independent.
UPDATE: I swapped the computer to another case to make sure there wasn't any shorting issue with the original case, and so I could get a better look at the motherboard. I didn't see any anomalies during the switch, but as soon as the system was in the other case I found myself unable to boot it at all. I tried swapping out all of the RAM sticks and tried booting sans GPU but I kept getting the same problem. I figured that the motherboard was completely gone and decided to move the CPU to another (older) machine.
However, with the CPU in the older machine, I started to get the exact same problem. I moved the older CPU into what I thought was the problem motherboard and now the newer system is working just fine. I did several boots and I think I can say with certainty that the issue is definitely the CPU.
So I guess the CPU is causing the shorting issue. Is there any chance of salvaging it? During the transfer I noticed that the thermal paste was pretty hardened and I don't have too much confidence in the heat sink - could this possibly be an over-heating issue? I never had any trouble with the system once it was booted, so I'm a bit perplexed by this outcome.