Random crashes/rebooting during Half-Life 2 and CSS - HELP!!!

[Ace No-Money]

For some reason I get random crashing on my computer while playing HL2 and Counterstrike Source! I know it's not overheating CPU, it will crash even while looking at the menu! I have windows 98SE, cant figure this out!
It says that the software caused an error after the screen freezes and then goes blue and displays the message in white letters. Is there a way to fix the problem without loosing the progress i've made in half life 2?
I just bought a radeon 9800 pro, will this fix the problem?

 

[DJ-CHRIS]

Probolly a RAM problem

Im also having problems in HL2 with random crashes, both memory and driver.

Im thinking the power supply is unstable.