Try it on another computer and see if you can open it up there. If it's still showing as 0 bytes then it's obviously a problem with the usb drive.

If it's a thumb drive (or some other solid state storage) then you're probably going to have to look into a data recovery service as they're going to have to remove the memory chips to access the information.

If it's an external case with a hard drive inside it then the best bet would be to open up the case and pull the drive out. Try connecting the drive to a computer (make sure the computer is off, then turn on) that way or through another external case. Be careful though, if the drive is making any funny noises or clicks then you could be damaging it and you'll need to again, take it somewhere for data recovery, also if the drive is not spinning at all (it's easy to tell) then you'll have to take it in. There's a chance it'll work fine though and your external might just be bad