It's unlikely that the memory card reader would suddenly die, but that's a possibility...
If you know the drive letter than the manager assigned to the specific card slot you're trying to use (ie: G is CompactFlash, H is SD, J is Memory Stick Pro Duo, etc), you can try going to the command prompt to see if it will even recognize the "drive".
Go to Start -> Run -> cmd
Type CD "drive letter" - So if you think the drive letter is H for the memory card you're using, you'd type CD H:\
If you get a "The device is not ready" message when you do this, you might have typed in the wrong drive letter. Also, make sure the memory card is pushed all the way in, and try again.
If it keeps saying "The device is not ready" then your memory card manager might be "dead". Even if the light on the front of it (if there is one) lights up, something may have happened to the wiring that connects it to the printer's chipset.