i will try to keep this short, as its a bit of a story and now i have no ideas left.
my problems started when i went on to aol broadband. what happens is , i am playing command and conquer online and all of a sudden either the pc will reboot, or the monitor will click off like its shutdown and i will have to reset at power. very annoying lol. when i was on normal dial up it never happend at all. then i went to broadband. it was doing it every 20 minutes or so and i was calling aol. and everthing but they said as long as u r online then there equipment is ok. i then had a friend who gave me a different modem, so i uninstalled the modem i got with aol and installed the one he gave me. for someone reason it worked better and it did not happen so often. then i tried to unplug my bb modem and plug in normal dial up. i was shocked to find it still done it. then i tried it off line and it still done it. i then removed the software for the bb modem and hey presto not a problem. .so this pointsto the the modem software. but how can it be i dont understand and i dont know what to do. i have done all virus scan, spyware, etc, change power supply, new graphics card. but it only stops happening when i remove bb modem software,and its been two modems as well, and other people seem to use them. its like i know whats doing it but cant understand y and what to do about it. i have windows xp home. 512 mb ram. 400 w powers supplt, ati 9550 graphics card, pc is not old and i know its to do with the modem software, drivers or something , i have even been thinking about buying a different modem to se if that helps. i just keep spending money with no result.i have all latest drivers all updates , have even reinstalled windows and just installed my game and bb just to see what happens.it still done it. thanks

I've had similar problems - let me guess is it a USB modem? If so get a mains powered USB hub (around £10) and plug your devices into that. It cured my problems. :-)