IT DEPENDS ON THE TYPE OF OPERATING SYSTEM YOU HAVE, ALL YOU NEED TO UNDERSTAND AS A USER IS THAT, YOU SHOULD BA ABLE TO KNOW THAT BEFORE THE PROBLEM OF ON/OFF ARISE, THERE MUST HAVE BEEN A SOFTWARE INSTALLED THAT DID NOT PASS WINDOWS LOGO. WHAT YOU HAVE TO DO IS THAT, WHEN BOOTING THE COMPUTER, PRESS F8 AND SELECT SAFE MODE, CLICK ON ALL PROGRAMS, NAVIGATE TO ACCESSORIES, CLICK ON SYSTEM TOOLS AND SELECT SYSTEM RESTORE.
TRY TO RESTORE IT TO AN EARLIER VERSION BEFORE THE PROBLEM DATE. AFTER RESTORE COMPLETE, RESTART THE SYSTEM AND YOU HAVE YOUR SYSTEM BACK AND HEALTHY. THAT WAS HOW I SOLVE MY WINDOWS XP PROBLEM.
HOPE IT HELP YOU OUT.