The Memory card slot is built onto the 2-slot PCB.Sometimes a few pins get bent out of alignment and the card will not make the proper connection.Remove the black plastic holder piece and try to bend the pins back with a flat head screw driver...make sure you count 68 pins,if some are missing replacing it is an option if you have the part. Anything is replaceable if you have the parts.
I'm not familiar with the 4 SLOT but an auction recently ended for a memory card attachment http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1125547042
-BB