I know from the topic you'll be expecting a question from a newbie about a BSOD or something, but please hear me out.
I built a machine about a year or two ago. About 4 months ago, when I switched the computer on in the morning, it got as far as the windows desktop before restarting. Thinking it was a BSOD (although I have set it to not automatically restart), I let it boot again. Same problem, only it didn't get as far this time. I tried safe mode - it restarted almost instantly. I left it in this constant reboot state for about 10 minutes, before finally it made it back to the desktop and was fine afterwards. Thinking nothing of it, I shut it down that night and forgot about it.
The next morning - exactly the same problem! I've tried a reinstallation of the operating system, and indeed Ubuntu Linux but both Windows and Ubuntu have the same problem, and sometimes it doesn't even make it to the point of actually booting the operating system, so I've ruled that out.
Sometimes it'll restart constantly about once a second for 20 seconds before making its way back to the POST screen. It's been like this every morning for about 4 months now, and I think it's about time I tried to solve it.
I've tried a different power unit, but that's all that I've really got at my disposal to test with. Memory checks (when my system is finally stable enough to conduct them) return nothing out of the norm. I'm guilty of slightly overclocking my CPU, but this doesn't corrospond to the time when things started playing up, and returning to stock/underclocking hasn't resolved this issue. My motherboard is running the latest BIOS available to me.
Can anyone possibly shed some light on this? I'm at a total loss as to what's to blame (I guess CPU and Motherboard are the likely culprits, but both are quite expensive to replace)
The PC is a Pentium D 950 3.4ghz with 3GB DDR2-667.
Thanks for the link. I looked through that earlier before I was going to post, was quite helpful in making sure I'd double checked everything, but alas no solution. Because of the strange nature of my problem, in the way that the system seems to 'heal' itself if I leave it for a few minutes, I often think that by making a change I've solved my problem until the next day I get the same problem again!
Although I have tested another PSU, I am going to buy another one shortly because mine is quite old, was dirt cheap and is stupidly noisy. Then I can 100% rule it out
I forgot to mention in my original post that although when it has finally booted it's fine for the duration it's on, as soon as it's been turned off for 6+ hours it has trouble booting again. Could this possibly be a thermal issue? Not in the sense of overheating, but flexing etc?
Sounds like a power issue to me, but may be something else as well. Try using the power calculator at Antecs website and make sure your PSU is supplying enough, maybe even return the CPU to stock speed as well. You might also try breadboarding the MOBO before you spend any more money, I.E., remove the MOBO from the case, placing on a non-conductive surface (bread board or even the anti-static bag the MOBO came in if you still have it), then re-connect everything and try booting the system and see how it goes. Be extra careful with the video card so that it doesn't move too much and cause a power spike or short. Download Speedfan and monitor CPU temps and see what they show (if you haven't done so already).
I've got a power meter that I've used on my system. I'm reporting a tad over 220w which seems about right for the gear I've got in there. Like I say, I've tried another power unit (400w) that I know is in good working order so I've pretty much ruled that out now.
CPU temperatures are normal, Pentium D @ 3.4ghz idles at around 55c - relatively hot in comparison to some CPUs now but never thought that to be out of the ordinary especially considering the stock fan was around 65.
The motherboard has been taken out and the case emptied of dust recently and the system was working perfectly for at least a year before the problems started, so I'm not inclined to think that it's a shorting issue.