There could be a number of things wrong! The first is that the battery is dead, the second the on off switch is faulty. The third is that there is corruption on the MBR of the hard disk, the fourth is that there could be a virus.
On most portable machines there is a very small hole (usually on the underneath) into which you can insert the end of a paper clip and press the microswitch to reset the machine to the state it was in when it left the factory. It may be worth trying this but I suspect you may need electronic diagnostic help.
M
