Ipod classic files .lnk

Hello,

I have an Ipod classic and I connect it both in PC and Mac.

Now, I plugged it into a PC once and all the files changed into .lnk files.

How can I change that without reformatting the Ipod and lose everything? and besides, how can I transfer all the music to a external hard drive? All my life in music is that in Ipod!

Thanks!