Can't download pictures from camera

Hello, I have a canon power shot camera which worked will with windows vista in the past. Now my computer doesn't recognize the usb and when I put the memory card in the computer card reader it wants to format it. I didn't format it before I took the pictures and I'm afraid if I say yes my pictures will be erased. Not sure why this is now a problem. As soon as I plug in the camera usb to the computer, the camera freezes. Please advise.