Your camera should have a facility to reformat the card. Try that first. If that doesn't work, get a card adapter and check the card out using your computer's disk utilities.
Once the card is recognised by the computer (if it is) right click on it and go to Properties and Tools and Error Checking.
If you can recall anything unusual you did immediately prior to the issue with the card, you'll know not to do it again.
If it isn't recognised by the computer, I'd return it to the retailer -- it may simply be faulty.