Computer will not recognise camera.

Hi, when i plug my camera into my pc, running windows xp it says "usb devise not recognized". I have tried different usb ports and it has worked previously but has now stopped working. i've tried downloading and installing the the driver but it still doesn't work, can you suggest a fix please?

I have exactly the same problem with SD700. Everything worked fine for a year (with iMac, OS X.4) and now the computer doesn't recognize the camera anymore.