did you remove the partition on the card it self? That would explain it. The card has to be partitioned for you to see it.
Here is the problem. removing the partition is effectively telling the computer, hey this card has nothing on it.
You may be able to try Recuva to get your files back on the card.http://www.piriform.com/recuva
You may require a partition on the card(just so the software can see the card). If you try this, it is important that and format you do to the card is a QUICK format so it does not reduce the chance of file recovery.
If you are not looking to recover, just create a new partition on the card(FAT32 if you) then you should be able to use it as before. You may also be able to format(Erase and make it writable) the card in your camera too.