Some stores can be real a******* when it comes to helping people. When I find that I don't go there anymore.
Anyway onto the camera problem. I will start with I know nothing about nikon cameras, but I do know about jiggling cables.
First, question is what end of the cable were you moving to get it to work? Camera or computer end.
You may not know, but I will ask. Is it a standard USB cable or one that is proprietary to Nikon? If it is a standard one USB you just take it to the computer store and buy another one. Test it. and if it works, then send yours to Nikon. Then return the other one after you get yours back. That way you can still use your camera and get a 'rental' to use.
If it is a Nikon Proprietary cable go to the store that would not help you and see if they sell just that cable. Buy it and do the same thing as I described for the normal USB cable.
I am sure you know, but I will say it anyway. Make sure of the return policy before buying anything. I say that because alot of tech stores are now charging a 15% restock fee.
You can also see if the camera is taking pictures and get a card reader for the camera memeory. That way you can just bypass the camera connector.
I would still check the camera conector, because if it is loose or bad that may affect other things.
That is about it for first steps. Please go ahead and ask any questions that you have on anything I wrote. I will try and remember to keep an eye on this thread. Also, please feel free to PM me.