ipod classic keeps won't sync to itunes; keeps being restored to recovery mode

i have a 160 gb ipod classic. i i bought it in june of last year and it's been great. but one day about three weeks ago i plugged it into my macbook pro i also bought last year and it keeps saying "itunes cannot read the contents of the ipod... go to the summary tab in iPod preferences and click Restore this iPod to factory settings." which i didn't mind... but it does that every single time i plug it in. it's won't keep any songs on it. it restores every single time... i don't drop it often, there's no water damage. it's been in a protective cover since i got it. it's in goo condition.. what can i do?