Chances are the card reader may be designed only for standard SD cards, and not SDHC. No problem though, as USB SDHC portable card readers are very inexpensive. If the reader still won't recognize the card, recommend you to attempt quick format outlined in the corrupted card procedures.
Also remember check to make sure that the write protect tab on the side of the card is slid toward the unlocked position (toward the contact points). Another thing to check is those tiny gold contact points on the memory card. Check them for any signs of dirt or corrosion, and possibly consider cleaning them with a q-tip, and a very small amount of rubbing alcohol. If that doesn't work, not sure what else to try, other than maybe trying to read it/format it in someone else's computer or camera. This way should help you out.