Thank you! 
Now that you point out where they are, I can see that someone's been inside it before as there is minor damage to the plastic casing around the first three points, where someone must have used a screwdriver that was slightly too big to release them. Maybe what they were trying to repair was this bit of plastic that seems to have become disattached. I don't know if you're familiar with the inside of these things or not, but if you are it's a three sided piece of black plastic which surrounds the rearward side of the silver disc at the front of the drive. It seems to be unattached on the right-hand side - should it just be pushed back into the track that it looks like it fits into? However, the spring that I can see inside the USB Zip drive on the left hand side of this bit of plastic is not there - presumably that is needed to make it work? Anyone know what this bit of plastic (and the spring) does? Presumably it is something essential to the operation of the drive...
Now that you point out where they are, I can see that someone's been inside it before as there is minor damage to the plastic casing around the first three points, where someone must have used a screwdriver that was slightly too big to release them. Maybe what they were trying to repair was this bit of plastic that seems to have become disattached. I don't know if you're familiar with the inside of these things or not, but if you are it's a three sided piece of black plastic which surrounds the rearward side of the silver disc at the front of the drive. It seems to be unattached on the right-hand side - should it just be pushed back into the track that it looks like it fits into? However, the spring that I can see inside the USB Zip drive on the left hand side of this bit of plastic is not there - presumably that is needed to make it work? Anyone know what this bit of plastic (and the spring) does? Presumably it is something essential to the operation of the drive...