Windows 2000

When you restarted, was this after you had disconnected the plug from the socket in the wall or did you just switch the PC off and on ?
Try disconnecting your PC from the electricity physically (pull the plug) for at least 15 seconds, plug everything back in and try again.

If that doesn't work, on starting the machine, can you hear any beeps, does the HDD run, do the ventilators turn ?

More info please - anything you hear or see is usefull.

Check your monitor cabling. If they are connected securely, try reseating the video card if you have one. Then reboot and see if you get any video.

Sounds like a vidoe cable was unplugged. The monitor power light should be an indication method or sorts. When the monitor is on and their is no video going to it, it should be an amber light - when video is going to it the light turns green. Video not going through then it could be loose cables or bad video card or bad mobo or bad bios settings, but it's not a windows problem if you can't even see the bios screens it would be a hardware or bios problem. Hope this helps.

I had something similar recently- it turned out the RAM was whacked.

Go ahead & reseat everything (assuming desktop)- all power & data cables & cards.

Get a new RAM stick- I'll bet that's the ticket.

Do as Breydel suggested and then carry it one step further. While you have power removed from the computer, hold the power button in for 1 minute. This drains some of the mobo capacitors that may be holding a charge. Now plug in the 'puter and try again. I've had this work in situations like yours.