How to fix the directional buttons on my PSP?

My son has a psp and when he put's a game in and try's to play it the character's start running in circles without touching an buttons. what causes this and how do iI fix the problem?

• Answer:

  It sounds like the analog stick is being pressed in a direction. See if the area around or under the analog stick is free of any dirt or sticky substances. (I believe you can take off the nub on top, but you should check elsewhere before you try to do that.) If everything is fine that way, you might try giving the analog stick a firm push downward. Not too firm, obviously, but the stick may have gotten lost off of the track. If that doesn't work, the problem is past normal user repair.