Wacom Cintiq 13HD No longer recognised

For some reason my Wacom is no longer recognised on my iMac. Using lates OS and Wacom drivers etc. I have tried ever suggestion listed on the internet but still it does not recognise it. It will mirror my Mac but the Wacom software can't find it. Basically I can't calibrate the pen. The Wacom software freezes, system preferences freezes when I click on the Wacom icon.

This is now driving me mad. Can anyone out there please help.

Thanks