HP LaserJet Enterprise 700 color MFP M775 series - Manual (Page 321)

4. Make sure that you do not have too many USB devices drawing power from the chain. Disconnect
all of the devices from the chain, and connect the cable directly to the USB port on the computer.
5. Check to see if more than two non-powered USB hubs are connected in a row on the chain.
Disconnect all of the devices from the chain, and then connect the cable directly to the USB port
on the computer.
NOTE: The iMac keyboard is a non-powered USB hub.
ENWW Solve product software problems (Mac OS X) 307