My home button is not working correctly,buttons dont register?

im not sure what the problem is exactly, so i'll do my best to explain. During an in game play, when you press the home/Playstation buttion, the home grey screen appers, like normal it asks if you want to exit the game, there is a yes and a no command, normally you would use the d-pad to navigate to the one you want then press X. the problem is that the left and right buttons wont move the navigation curser between the yes and no prompts. this leads me to think that there is a problem with the d-pad itself. but the d-pad works perfectly fine during in-game experinces and even the psp out game home navigation "music/photo/game/settings/network/etc. im very confused and im not sure how this problem was caused. via its not my psp is my cousens and im fixing it for her.