how do i stop my computer from freezing !?!?!? plz help

it all started on the 2nd of december cause i was goin to a lanparty .
my computer is not the best , but it still is okay i guess .
well anyways , i only had 128 mb of ram so i uped it by 128 mb so i could play cs on my comp . thing is it was windows 2000 and it kept freezin so i downgraded at the lan to ee if that would help . Well as you can imagine it didint help and im sitting here sraching my head to see whats wrong with it .
here are my system properties :

Intel(r) Celeron(tm) Processor
224.0MB RAM
Quantum 30.00Gb Harddrive
ASound ex press pci sound card
Nvidia 4000 video card
Windows 98 SE (wow , its lame )
*I also used anti-virus , and checked for computer errors and fixed them already , please reply to me asap thx , d34dcell

nm found it

i found the culprit , seems my graphics card got shot lol , thx ne ways guys