How to fix Volume issues in PSP Portable

How to Fix a PSP Volume Button through Software
Check to be sure that your PlayStation Portable's AVLS (Automatic Volume Limiter System) is turned off.
Start your PSP without a game in it. Choose "Settings," then select "Sound Settings." If the AVLS option is "ON," turn it "OFF."
Check to see that your memory stick is inserted properly if the sound still does not work. This often interferes with the volume control. Remove the memory stick and reinsert it.
Perform a hard reset of your PSP if the volume still does not work. To do this, first unplug your PSP and remove any games or memory sticks. Then remove the battery from its cavity on the back. Press and hold any button for five seconds, then reinstall your battery.
Move on to hardware solutions if none of the above options work
How to Fix a PSP Volume Button through Hardware
Remove your PlayStation Portable's battery pack, any games and memory sticks. Unplug it.
Unscrew all five screws that hold the faceplate onto your PSP. The fifth is hard to locate, so find it just below the screen on the bottom edge.
Clean the button heads underneath the volume buttons with a small cloth. You should also clean the Home button nearby as this often interferes with the volume button.
Return the faceplate and screws, and test your PSP.