Apple usb SuperDrive disabled from imac21.5 with message using too much power

During initial use device operated for short period but was then auto disconnected with message " USB devices disabled". " unplug the device using too much power to re-enable USB devices"

device description; Apple SuperDrive , p/no. MD564ZM/A

desk top; iMac 21.5/2.7QC/2X4GB/TB/IRISPRO, P/no; ME086X/A

Have closed down computer several times for extended periods, and when restarted and super drive connected, same message has appeared, with nil operation of super drive.