sony vaio laptop problem

can anyone tell me why my laptop shuts off everytime i turn it on it will power off after only a minute or two. after restarting it about 10 or 15 times by taking battery out and up pluging ac from computer over and over it will finally sometimes sign on line. never the less it will never stay signed on or even keep power on for more the 20 at a time.rarely does it stay on that long. do i need a repair disk or restore disk or what the heck? thanks to any one who can help.