Hello..
I have 3 PCs , I've just installed a fresh copy of windows xp sp2 on them, they worked fine for 2 days, and suddenly , when I power on the PC , the fan works and leds start, but the monitor doesn't show anything,, what is the problem?? I tried another monitor and the same problem...

Please reply as soon as possible

Is this just one 1 PC, it sounds like your video card may have stopped working

Since you have tried this with 2 "known" working mointors, see if you can get a "known" working video card and exchange it with the one that seems to have the problem to see if that is the issue with that particular PC

I would agree with seahwk83, your video card on the PC is probably shot. I had the same issue multiple times and replacing the video card solved my issue.