Songs not adding to Itunes Library

I'm trying to add some songs to my iTunes library, but it's just not working. I've never had any issues before. It's not even giving me an error message, it's simply not adding them.

The songs are MP3 format, I'm using iTunes 8, and my OS is XP SP3.

I've tried file>add folder, file>add file, and I've tried dragging them onto the library. There are no other songs sharing the same file name. The songs play from beginning to end just fine in WMP.

Has anyone experienced this problem before or can any of you suggest a work-around?

Thanks