computer automaticly shutsdown/locks out on me

control_tower_here

ok my computer shuts down sometimes, someitmes when iam surfing the internet, or sometimes when iam not even doing anything and i leave it for a sec and it shuts down. iam on a pc. the hard drive power light button thing turns yellow instead of green and my screen turns black, the screen power button turns yellow also. when i move the mosue or press buttons on my keyboard..nothing happens it just stays black. i pressed the 1st button on the 4 little button on the screen, and a message comes up saying when in power save mode press computer power button ot move mosue or press a button on the keyboard. i do it but it still doesnt start up. so i end up having to shut it (by pullin the pug) and turning it back on. i did a virus scan but it didnt have anyhting. i have mcafee security center.


some info to add about my comuter:
Dell Dimension DXC051
Intel (R)
Penium(R) D CPU 2.80GHz
2.79 GHz, 0.99 GB of Ram

rmg1

Have you checked the power optionsetting in control panel?
There are 4 settings, monitor/hard-drive/system standby/system hibernate.

You might want to check the settings on those to make sure they've not gone to very small values as that can cause the problems you're having.