Can't transfer songs to itunes.

Hey,

I'm trying to add songs to my iTunes library, I've got about 500 .mp3 and I tried dragging them in and only 100 get added. I've tried doing this individually and only the last 100 only ever get transferred. And when I try to play the first 400 files, they won't play with iTunes but work fine with any other programme.

Any ideas?

Let's see if I've got this right ...
1. you can transfer only 100 tunes at a time,
2. you try to play the first 400, but they won't work.
So, you've managed to transfer 400 - 100 at a time - but they won't work.

"Any ideas?" Very few actually, but in your situation I'd try:
1. checking through all the iTunes prefs to see if anything there is affecting playback,
2. repairing permissions, preferably using OnyX Titanium Software appropriate to your OS version.

How are you transferring the files to iTunes, and which other applications play the .mp3 files okay?