My Computer Randomly goes into standby. Please Help

[Bizzoyce]

Ok, heres the problem. My computer decides to go into what i think is standby mode at random times. I could be downloading things, playing games, or just restarting my computer. My monitor flickers off but my computer is still on and the only way to get it out of that is to press the reset button. Any information would be great. Thanks

 

[Tedster]

do you mean it freezes? or shuts down? be more specific