Computer Shuts Off with Games (seems related to hd4870) *fixed*

Sounds like a PSU related issue, but 750 watts is more than enough. You specs load will take around 450-500 max. Can you try swapping another PSU from a friend?
Next thing I will look into is the RAM. Would borrow a friend's RAM and test it out with just 1 bank only.

Is your rig OC'ed?

DVD drive idle is like... 5-8 watts only....lol
Take your vga card to a friend's house and try it out then.
A Q9450, 4GB ram, 2 HDD, 4870x2 crossfire uses around 550/600 watts load. - off the wall is 800
So your PSU is actually fine. Might be a problem with the amps on the rails.

If you want to test the RAM, try using 1 bank of ram only. I've had issues where MemTest works fine, but gaming doesn't.

Well, it wasnt due to the configuration of cables. I wanted to make sure I didnt have anything loose in there.

The current psu is a replacement for the same brand/model, which broke very shortly after I had purchased it almost 2 years ago. Wonder if my thermaltake 750w is up to it's old shinanigans. Has a 5-year waranty parts&labor... I really hate waiting for sh** like that tho. Rather play FO3 in dx10...

I have been running with bios set to default ever since these problems began. I noticed that advanced/advanced chipset settings/memory remap feature was set to enabled. I looked it up, and that feature is only meant for 64bit OS. I am using vista 32bit. I turned it off, but no luck, still crashes after playing for a little while. Is it possible that the default setting could have damaged the card/mobo? (would be the dumbest thing I have ever seen in BIOS if it is.)

I will try obtaining a test psu, but I doubt I will find anyone who even has the minimum requirements for this rig, (without spending $$$).

Otherwise, I will try running memtest on it, see what happens. (making the disk right now.)

Thanks for the replies and ideas. Anyone else have any?

i dont think its ur PSU, i think ur chipset is running hot and the pc is shutting down to prevent damage

After 5 hours of running Crysis, I am happy to report, my problem appears to be gone.

After installing the new antec 1000w power supply, no more random shut down/reboots. http://www.newegg.com/Product/Prod [...] 6817371012

I ran memtest86 for 18 cycles no prob, and heating on the entire mobo has been fine through testing.

The weirdest part about all of this, is that gpu-z shows my hd4870 actually running, over all, lower temps now. I barely broke 60c this time under heavy gfx loads, where as before it would really work that fan to stay around 65c-70c. I still dont like the fact that fan control appears to be largely software reliant, as on boot ups where I was in bios/dos/whatever seems to really heat up the card, showing a temp of 77c when I finally get into windows. Time to find a new heat-sink, but that's a topic for a new thread.

On the old PSU, the PCI-E power cables had a wire in all six of the ports. The new one has only 4 out of the 6 ports wired. Not sure if this has anything to do with it, I may in fact be underpowering my card (pardon my lack of power cable knowledge.)

Everyone I spoke to agreed that my psu should have enough power, except a couple of people who speculated the psu may be having some problems (seems so). I was also told by somebody at fry's, that he would put at least 800w on this rig (seems so as well).

I had already returned the original Thermaltake shortly after purchase, using the manufacturers waranty, as it burnt out after about a month. The replacement it seems, may have had some issues too. Still under waranty, I might just get it replaced and keep it for future self inflicted head aches.

Thanks everyone for the info, and I hope this helps those of you who are suffering from similar issues.

*Please note, I did not get the model with the 6 12v rails, as I had originally stated I would be buying. This one has 4, and works great.