itunes not recognising ipod touch

Hi - seen this problem in a few forums and tried all the solutions except reinstalling itunes. Have had no problem updating and syncing ipod touch with itunes (on Mac OS X) via USB cable. Suddenly not working. The ipod doesnt appear in itunes, 'sync' in 'devices' is greyed out. Have rebooted ipod and tried everything else, very frustrating. From memory have done couple of itunes updates since last ipod sync, so is that the problem?

Bertie