Well with this wealth of information it is hard to say.
Have a read here, post a LOT more details about the machine, what happened prior to this, and we'll be awaiting the next burst of information.
http://www.computerhope.com/cgi-bin/yabb/YaBB.cgi?num=1144733358
I have scan the virus, check HDD error, and system restore to earlier.
I also tried to plug only keyboard ,mouse ,monitor only. with one SDRAM.
I even change anothe SDRAM.
But the problem still exits.
I tried to replace another power supply (same =180W as my original power supply).
It also can't help.
I reset CMOS just now.
PC keep on reboot to BIOS after setup my CMOS.
Worst n worst now, it can't boot into windows XP.
Sometimes, the power button LED turns to amber ,then green,boot to BIOS,then amber again.
I feel that the hard disk very hot.
Will hard disk cause tis kind of problem?