PC freezes, What do i replace?

[gimli of gloin]

Alright, this first started happpening about a week ago whilst playing WoW. Basically my computer freezes for about 10 sec then unfreezes, then just keeps doing this while playing. Before this started happening i always got glitch like things during the game, which i found out where because of overheating graphics card. Now at present my PC will load to the user screen then freeze. I have cleaned out all dust from the graphic and cpu heatsinks and i have placed a house fan into the case and it still happens. Now looking at both heatsinks i could see very little heat transfer stuff (it had been worn away). So im thinking i will reapply that. I was wondering if that doesnt work what should i replace. My system i would guess to be 5 years old.
400w PSU
2.6 Ghz Celeron such and such
6600GT 128mb (upgraded)
512mb DDR400 ram
ASUS P4533-X

Should i buy more fans? Should i buy another PSU? Should i use this PC as a doorstop and buy another? Is it a Hard drive Probem?

Thankyou in advance for any and all help.

 

[silence782]

If you have a lower-end video card, that could be causing the problem, or the game just could be lagging when you play online.

 

[gimli of gloin]

Well my video card was causing glitches before. but now the computer is just freezing when WoW isnt even on, Like just after i start up my computer and get to the user screen it freezes. Also my graphics card is really hot after like 5 min of the computer being on. :S i think it is a PSU problem.