You can either
download a newer system software
or clean the buttons on your psp
or take it to game shop( if it is in warranty) to have it serviced and let them see if there is some sort of hardware fault
if you have had it for ages then it could just be that the psp is packing up because of old age
it could be time to trade it in at game station( they give you loads of money if you say somewhere else in the same street gave you more) and get a new one