很奇怪的問題,請示高手

我開不了機,但是MOTHERBOARD GREENLIGHT IS ON,AND CPU FAN
IS OK FOR SURE,MY COMPUTER WAS FINE BEFORE I TURNED IT OFF YESTODAY,AND WHEN I CLICK THE POWER BUTTON,THE CPU FAN SHAKE AND STOP,POWER SUPPLY SHOULD BE OK CAUSE MOTHERBOARD LIGHT IS ON,SO DO YOU KNOW WHAT THE PROBLEM
IT IS ?