Computer tech support

[Jason McK]

My Desk top has been rendered useless. Please help

I currently have a P4 3.6G PC with 1.5G RAM, Brand new Power supply, Brand new 500G HDD.

What is happening is when the system boots is goes past the post and loads windows. At what seems to be a random time the system freezes. Total lock up. Some times Windows is up and I've launched software, some times it will lock up before windows it up.
CPU heat sync was clogged full but now temp does not exceed 30C
AGP graphics card's heat sync was also jammed with dust.
It appear to run fine in Safe mod.
This leads me to believe it may be the video card. (just upgraded my Monitor to a 22" LCD) but It's AGP so replacement is a waste of money

Any help would be very help full

thanks
J