Olympus SP570-UZ......problem dow...

Olympus SP570-UZ......problem downloading pics to pc from camera. Previous no problems at all. Then all of a sudden, after plugging into usb2, camera displays 'transfer images', click, 'wait one moment' appears on camera screen..........and nothing happens. Pc says 'does not recognize that a device is connected to the computer'. I can view the pics on the camera screen as normal but just can transfer them.