Okay, first off, it's my brother's computer. It's a Dell XPS 700 (or 710? - don't really know). It's a BTX full tower case.
CPU: Core 2 Extreme x6800 dual core
MoBo: OEM Dell branded
RAM: Samsung DDR2 667 PC2-5300 (4x1GB modules)
-> assuming OEM as it was fitted in Dell case when he got it.
PSU: OEM 750w
Very dusty and using compressed air and vacuum to clean it out. It's been neglected since he bought it (in 2007).
Problems began with the monitor going to sleep and fans going off. Power off/on and it starts working again. But then the problem surfaces again in a few hours. Thought it might have been a gfx card issue, so swapped out the SLI cards and put in my old 8600gts. Everything seemed fine for a few days. But the problem seems to have escalated. Now it starts to fail POST half the time. Monitor will remain in sleep mode, but fans will be spinning.
So I decided to run Memtest86+ v4.2. Well, it gave me 4 errors after 1 pass. So I now start to troubleshoot whether it's actually RAM, Mobo or PSU problems. Well, it turned out as I pulled out the modules, there was a lot of dust on them and some of it in the slots. So I used compressed air and a vacuum to dislodge and suck it up. I cleaned it out the best that I can and started running the tests.
Started with 1 module in single channel:
A1 slot: 1 pass, no errors.
B1 slot: 1 pass, no errors.
A2 slot: 1 pass, no errors.
B2 slot: 1 pass, no errors.
Okay, so I can assume the mobo is okay and 1 of the RAM modules must be bad.
Well I tested all of them in the A1 slot with 1 pass and none of them produced errors. ??? Okay, that's weird. Maybe there's something wrong with the dual channels running.
So I popped in 2 modules:
A1/A2: 1 pass, no errors.
B1/B2: 1 pass, no errors.
So I go in and pop all 4 modules in (thinking that the lodged dust may have been a factor for the previous errors). Well, errors popped up again. So, now can the PSU be causing this problem? Or is there something wrong with the mobo running both dual channel memory?
The PSU would not be causing the RAM issues as they draw very little power. It's possibly a mobo issue. You might try running two DIMMs in a dual channel config for a few days to see what happens. Troubleshooting these types of issues can drive one insane...