Thanks.
We finally figured it out.
I have just sent back my PSP to Sony for an exchange because many of the games we have no longer will play.
Maybe you would know.... When we were in USB mode and trying to upload to the PSP, the machine would show we were transferring files, but when we would review the Music folder, no songs were displayed. Of course, becasue they were not mp3 files. However, our memory was being used up as if the transfer was successful. Any ideas??