From your post, you previously could upload?
You should eliminate the possible problems. Take a picture, and see if it appears in the USB folder when you connect to the computer. If it does, then your older pictures are gone, I'm afraid. If you do not see the new picture, then 1. Maybe your camera is faulty (Or new battery, old battery no longer charging?) or 2. The memory chip itself may be faulty. If you have a card reader, you can check that the USB cable and/or the chip is OK.
Last, and obvious thing to do, would be to try it on another computer?