Why won't My PSP read UMDs?

My psp does not read some of my umds but reads others. Of the ones it wont read, a few are nearly brand new and in great condition. It does however, read some umds that are in poor condition. I am very confused. My psp has never been dropped...

• Answer:

  Do you get any kind of messages at all, or does really nothing happen? Keep in mind that to read some games, especially recent ones, your PSP needs to be upgraded to play a certain game, which can always be done via the game you're trying to play. You need to recharge the battery to max for some reason I don't understand, then load the recent PSP version with your game, which takes a bit under two hours. If that's not the problem, then I really don't know. :( I would need to hear more details.