Thanks anyway guys but I've sorted this now.. For anyone having the same problem after a backup here's what to do..

Highlight your Ipod in Library
Click 'Music' tab
Then check sync music box.
Click apply at bottom right of iTunes.
Message will appear stating that Ipod will be erased and new library added. Click yes and your ipod will be erased with the whole library (plus any latest additions) now synched to your Ipod.

Hope this is of use to someone..

Regards,

Joe.