Instructions
Check the mute settings. Clear any current sound settings by pressing the audio button on the face of your PSP. Test to see if this solved your problem.
Test to see if you accidentally turned the volume all the way down by raising the volume level and checking the sound quality.
Remove headphones from the headphone jack. Having your headphones plugged into the device will prohibit sound from coming out of the actual speakers.
Make sure the AVLS (automatic volume limiter system) is turned off. The AVLS is a safety precaution that limits the amount of sound that can come through headphones and speakers and may severely cut back on the sound quality when turned on.
Disconnect and reconnect your memory stick. Sometimes when the memory stick is not fully connected, it can interfere with volume and game quality.
Check whether or not your device is connected to a video output cable. In the event that you are connected to video output, you need to control the volume from the video device you are playing through.
Try resetting your game system. Make sure you remove games and save devices before doing this to avoid erasing your saved settings. Remove the battery pack from the back of the PSP device. Hold in the start button for five seconds while the battery is out then replace the batter and restart your PSP. Test your volume to see if it's been restored.