iMac stopped recognizing USB CF card reader

Troubleshoot to determine if it is the card reader or the computer.
- do a fresh restart of the computer
- try plugging the card reader into a different USB port
- try plugging in other USB devices to see if they are recognized
- try a different USB card reader
- try a direct connection from your (camera?) to the computer

The above should tell you if the problem is with the card reader or the computer. Although the problem could also be the CF card - they do fail.