laptop not bootup, no display - please help!

The story is: I installed Kaspersky Anti-Virus (downloaded from one chinese website, should be find), connected online for update signature. Following Restart request, the laptop stop at a message that it was installing a Win xp update (I set it for autoupdate) and will shutoff itself after install. I left it there and when I came back, the screensaver was running (maybe the standby was started), I moved mouse and clicked something like to shutdown. Then screen showed bluecolor sentenses on black background (or maybe wight sentenses against blue background). I didnt have enough time to catch it before it shutdown.
I waited for restart, no action. Press the power, screen displays nothing. I can hear hard drive running, fan moving, CD drive running. Nothing else.
This Toshiba Satellite 3000 can play CD without bootup. I tried it, CD still can be played. But I put Win XP disc in, no reaction. I change to floopy drive and insert boot disc, no reaction. Hard drive fix floopy disc, still no reaction when try to bootup.
So I changed a working Harddrive, still the same. And the old harddrive works in an enclosurer.
I reinstalled RAM, no improve.
Insert USB flashdrive, the light doesn't turn on.
Could it be the CPU, or motherboard?
Any kind of suggestion will be greatly appreciated!_:'(