Freeze/sound loop in games.

Recently I have been having problems, with what I can only assume is the videocard.

When I play a game for a long period of time (Anywhere between 5-11 hours), say, Assasins Creed or World of Warcraft, after a certain period of time, the screen will completely freeze, and whatever sound was playing will loop forever. The only thing to get rid of it, is to reboot the PC.

Now i've tried hard to figure out what it is, but i'm clueless as to what it could be.

I tried:

1. Format the PC, everything reinstalled from scratch, but didn't help

2. Tried the latest Forceware drivers, both normal, and beta, but no results.

3. Scanned HD for problems, but didn't find any errors

I checked speedfan for my PC temperatures, but it didn't show anything amazing, the only 2 it showed as red were the
motherboard, and the videocard. MB at ~49, GPU ~68 idle. The rest was all relatively low ~25/30 degrees Celsius, but I was told the GPU
temp is appearently normal for 8800 cards.

My system is as follows:

Motherboard: Asus P5N-E SLI
GPU: XTF 8800 GTS 320 Mb
Processor: Core2Duo 6600
RAM: 2x 1GB Buffalo I believe
OS: Windows XP Home
Sound: Creative SB Live!
PSU: Zalman 550w

None of it is overclocked, never was, and I've had this PC for over 9 months, and these crashes only started happening a few weeks ago.
I cleaned the PC completely, but it didn't seem to have helped. It wasn't that dirty anyway.

Any ideas on what it could be? I'll take any suggestion I can at this point. This is pretty damn annoying.

Thanks.

Jam it back in, in the dark.

My old 6600GT did exactly the same when it overheated. Give the graphics card a good clean to get rid of any dust that has built up. Or if your brave enough get some Arctic Silver V and reseat the heatsink.

There's nowhere I can't reach.

GPU idling at 68C sounds pretty bad to me. My 8800GT idles at around 54-60. It could be that, I'd suggest getting an aftermarket cooler.
Have you run memtest for a night or so to see if you don't have any problems there?

My old pc did that a lot, but my GPU temp (regular 6600) was a hell of a lot lower than my new one. It probably had bad ram, I never bothered to check since it was a 4 year old pos anyways.
My current north bridge is at 48c, apparently that's fine. My old one was at 38-42c. Don't think that was my problem...

This thing is sticky, and I don't like it. I don't appreciate it.

I tried a lot of different things, even memtest and after running that for 14 hours it found nothing, but I removed 1 stick to see if that helped, and hasn't crashed since. It could have been the ram, but perhaps not.

I was able to play for 3 days straight playing extremely long gaming sessions, sometimes over 12 hours, and it never happend again, so at least this leaves out the overheating and perhaps the videocard entirely, but today something happend again, basically instead of the screen freezing + sound loop, i got sound loop and the screen turned black, with "no input" on monitor, so not quite sure what to make of it.

I'll try testing the other stick of ram see if it happens a lot with that stick.

I am a dolphin, do you want me on your body?