Open feeder so you see flatbed scanner. The scanner unlock latch is upper L of the big platten glass.
Try locking then unlocking and restart.
If its making a grinding noise remove the two screws holding the cvt glass/scanner lock latch in place and remove it the power on and reinstall. The screw heads are hidden under silicone caps
If there is no grinding noise your scanhead belt is probably broken. You can see that through the glass. It is a black toothed belt that should be under tension attached to scanhead. If its drooping you need to replace it
Attempting to set up printer and get this message: “The scanner is locked. Please check the lock underneath the scanner, move it to the unlock position, then touch the confirm button.” I have looked everywhere I can think of, including actually tipping up the whole machine to check the actual underside, and searching the internet for tips and still I cannot find this unlock button. Help? Xerox WorkCentre 4150