X1900xtx freeze/reboot/VPU recovery

My machine is running all day long, and been doing so for the past years.
It consists of.
p4 650 3.4 ghz
Abit ig-80
2x512 mb corsair pc3200
ati x1900xtx 512mb
3x sata drives
chill-innovation cp-450a4 450w psu

I've played red alert 3, car games, asassins creed and more, no problems, this was a few months ago tho.

So the other day i wanted to play red alert 3 again, it ran fine for a few min, then suddenly the screen went black and restarted, and the vpu recovery message had popped up from the catalyst control center, first i just thought it was a glitch in the driver, so i rebooted, but same issue, so maybe it was the game.
I then installed turok, but i get the same problem, it even reboots by it self now and then, but it runs fine for the first 5 min.

so reading the internet, aparently quite a few people are experiencing this issue.

My computer has just been reinstalled a week ago, latest driver everywhere and win xp with sp3, i runs 100% fine doing all other tasks besideds gaming.

so i was thinking, could this be the psu reaching it's limit because it has gotten old and worn out?
i tried the psu calculator. http://www.extreme.outervision.com/PSUEngine

which says my hardware would use around 398w under 100% load, and my psu is 450w.

i tryed out atitool, scan for artifacts, if i do it with the normal clock 500/594 it runs without any problems, just now it's been going for 40min, but if i use the 3D clocks 648/774 then the vpu recovery will kick in after little over 1 min.

I tryed using drivecleaner to remove everything and then reinstall the drivers, but no effect.

I just can't figure what is wrong, any help would be apreciated.

i havn't tryed doing that before, but is that possible with just regular tools?

I actually have some Arctic Silver céramique, guess i can use that.

jaguarskx, thank you.
just applyed new paste, and atitool ran for 1½ min and still going, so it seems like you where absolutely right.