A constant OS crash... with variable effects! Please Help!

[Furius92]

Ok, continuing my journey into Vista, I've hit my worst problem yet. Every single time I log into Vista (Home Premium) I crash within 10 seconds of reaching the desktop to a.... sometimes green, sometimes yellow, sometimes greenish yellow, sometimes light and dark green vertical striped, screen. I can't do anything, no response to anything at all. The only option is to hit reset. Specs are as follows:

Intel Core 2 Duo E6300 (mult. @ 6 x 400 = 2.4 GHz)
2 GB Corsair XMS2 DDR2 800 @ 800Mhz
Asus P5B-E
HIS X1650 XT IceQ Turbo
Creative SB Audigy SE
Seagate 7200.10 400GB HD
Asus DVD+-RW and DVD-ROM drives
Corsair 620w PSU
Antec P180B
APC UPS running PowerChute software

I had it running fine, OC to 2.4 Ghz with no problems. I was able to run Supreme Commander, but Oblivion would crash quickly. So I turned off UAC so I could run RivaTuner and underclock the video card (it comes OC 55 Mhz on the core). I set Rivatuner to run on Startup. I turned off the PC at the end of the night.

So today I turn it on, I log in, and almost immediately after I see the desktop I crash to the screen described above. Then, after I try disabled legacy USB support and running the CPU at 1.86 Ghz (or whatever standard is, 7 x 266), it kept doing the same thing. I disabled Rivatuner start on startup while in Safe Mode. Then, I would get nothing at all on power up. The monitor would go to sleep. I reseated the video card and now I am back to where I was with the crashing. I can't think of what to do... I need some serious troubleshooting here. Please advise. I hate not being able to use my $1500 computer.

[glc]

Test your ram with memtest86+, if it tests good I'd suspect a defective video card.

[Furius92]

Thanks GLC, but I actually did resolve it. I used system restore, and apparently it was RivaTuner that was messing with Vista. After the restore, it wasn't set to start on startup, so I tested an underclock of 15 MHz on the video card core... as soon as I hit test, I had the same crash screen. I guess when I changed the setting it didn't really change anything. Anyways... know of any overclocking utilities that Vista likes for ATI cards?

[glc]

Why are you trying to overclock the video card?

[Furius92]

I'm actually trying to underclock the video card. The HIS card comes factory OCed to 630 MHz core instead of standard 575 MHz. I want to drop it to 620 MHz or so because I have read this is the only way to maintain stability in some games. I have had frequent crashing problems in Oblivion, and have tried several other things. I have yet to find a utility that works under Vista to OC my ATI card.