Ive dragged a song(s) to my Ipod, is says its copying it, but its not actually doing anything...

I had copied a heap of music manually on to my ipod touch when I frst got it. I have since tried to again, and it shows the songs on itunes, but with the loading sign next to it, but it never actually tries to copy the song across. Its doing this now to anything I try to copy across and cannot put any more music on my ipod!

please help