Problem with opening games like GW and Warcraft

[stealthstud]

hey guys. i built a custom computer for being able to play high definition games and do normal comp stuff at the same time. However, one night, whenever I open a game that takes up the whole screen, like in Guild Wars and Warcraft 3, my program hangs almost immediately and my computer then hangs too. A noise emits from the computer when this happens. Can anyone help me eliminate this?

[spyder003]

Why are you trying to play games and do "normal" stuff at the same time? What type of programs are you running? The biggest thing that's going to help you there is a ton of RAM.

[stealthstud]

i apologize, you misunderstood that sentence. I meant that i made a computer so i can do my work and also be able to play games - not both simultaneously. I have 256 MB sticks x3 which should be enough RAM anyways.