You could try checking that the card reader cables are securely connected.
I occasionally have a problem with my card reader. In my case it is caused by a build up of static electricity. My PC manufacturer advises -
Shut down the PC completely and switch the small power switch at the back of the PC to the 0 position if applicable. Then (with the PC still connected to the mains) press and hold the Power Switch on the front of the PC for approximately 30 to 45 seconds. Release the front Power Switch and return the small power switch on the rear of the PC to the | position. Then switch on the PC as normal. When you switch it back on you should find the card-reader icons have returned.