Ahhh mate.... I had this problem and my specs were similar to yours - but unfortunately it might not help.
Processor: q6600 2.4
MB: several. both asus and gigabyte
Ram: several. corsair and kingston (1 was 2x2gig, 1 was 4x1gig 800mhz)
HDD: several. Samsung, WD, Seagate
case/psu: Antec Sonata III w/ 500w psu
As you can see, I tested alot of hardware to try to solve the problem. 3 HDDs, 5 mobos (2 models of board), 1 replacement case and psu and 3 pairs of memory sticks (two different brands). The entire PC was also sent to ebuyer (component retailer), twice, and both times they failed to find the solution. I even left it with a specialist PC store for 3 months. The reason why they were both hopeless is that it was such an intermitant problem, so finding the culprit is very difficult.
Not trying to depress you but it sounds like you have something similar. (Don't worry it appears to be fixed now - 1 year later!)
I've got a few questions:
1. Are you sure its sleep mode? That's what I assumed too. It might not be. Turn off sleep mode and leave your PC on for a day (or 3 - mine could be stable for up to a week). What was happening on mine is that the system was restarting and then hanging just after the logon screen - but it took me weeks before I actually worked that out because my monitor would instantly go into power saving mode, making it appear like a sleep mode that I couldn't wake.
2. After it has crashed and you restart the system does it always boot? Or does it sometimes hang?
3. Have you had any error messages from Vista?
I'm no expert at all mate, but I spent a **** long time on this (on and off for a year). I initially thought it was a memory problem, but I tried XP with 1 gig of ram (alternating 4 sticks), I performed a memory test, and ultimately a new brand.
If you've got something similar to me then I very much doubt you'll be able to google an answer - i've looked for ages.
First off - does your graphics card have two power cables? Are they plugged into two different power cables from the psu? (ie not using two molex plugs from the same cable). Might seem odd, but this is one of the only differences between my old unstable PC and the stable variety.
Hope this helps.
PS: basically the specialist pc place admitted they weren't sure, but suggested replacing the MB and gfx card. Seems to have worked. Depending on your consumer laws/rights you might be able to do what I did and send it back saying its not what you want and choose another model. That is if you have the same problem!
Thanks for the reply. To answer your first question, I'm not 100% certain it is sleep mode. I do know that once I disabled sleep mode, I do not get a crash over an 18 hour period - I generally shut down my computer before I go to bed. I'll try leaving it on for a few days to see what happens.
When I had sleep mode enabled, most of the crashes were during, or coming out of, sleep mode. But not always. It would sometimes crash in the middle of World of Warcraft. Since I disabled sleep mode it has never crashed .
To your second question, the system always boots.
I do get blue screen error messages when it crashes, often IRQL_NOT_LESS_OR_EQUAL but not restricted to it.
My gut feel is that it is related to my GPU. I'll check the power cables as you suggest. I may try reseating it as well.
Obviously it would be nice to have sleep mode working but I can live without it as long as it doesn't crash.
I know this topic is already a month old, but I've expienced exactly the same problem.
Intel Core I7 920
6 GB's OCZ Memory 1600
Windows 7 RC 7100
I noticed it yesterday, my system was shut down, when I went to the store real quick. Sleep mode is set on 30 minutes and I was gone for about 40.
Today the same had happend, I was watching the Grand Prix race and saw the monitor going into standby, no problem.. 20 minutes later I heard the harddisk shutting down. So naturally I though.. oh it's just sleep mode, but when I tried to get it out of sleep, it wouldn't come. I had to re-on the computer and at boot windows said it did not shut down correctly, just as reported in the event log.
When I put the system in standby manual and immediatly pressed a button to get it out of standby, it worked perfectly. I tried it again and left it in standby for 5 seconds, but it wouldn't come anymore. It had crashed!
For now I just disabled the sleep mode in Win7. But 1 strange thing I had it set on defragmenting my drive the first time it crashed. Maybe a bug, but in my knowledge a system should not be able to go to standby when defragmenting.. but that on the side.