If the laptop card reader can't read it either, it sounds like the actual card is to blame. I'd suggest calling up sanDisk and seeing if they'll send you a new one.
Blast slot with compressed air, especially if you use phone without the blank in thus mentioned slot for it has no cover. If this has no affect, than it is a hardware problem. Go to a Cingular store that has someone that knows the phone, I'd call ahead. Check the online manual, maybe.
Usually answered in minutes!