My Sansa skips the songs I put on it, what can...

Question

A couple days ago i put some songs onto my Sansa e250, but i couldn't listen to them, when i disconnected it from the computer. I would click on the songs and it would just freeze for 2 seconds and skip to the next song. Then i connected my Sansa back to the computer and I put the same songs again onto it again. It appeared on the screen when i turned it on, but i still couldn't play it. What can i do?