Hi James, whilst I am waiting for your response I wanted to answer your original question with a few suggestions for you to consider.Firstly, if you are attempting to charge this camera for the first time, and are following the instructions that are listed within the user manual that came with the camera, then it appears that there is an information error. Please visit the following link to see the correction:https://support.nikonusa.com/app/answers/detail/a_id/16862If this isn't the first time you are trying to charge your camera, and it has worked previously in the way in which you described then there are 3 things you could potentially try to see what part of the process is failing.
If you have a spare USB cable that you use for another device that can also fit your Nikon camera, please try this out so we can rule out the cable. Since you have tried more than one computer, it's safe to assume that your USB port is working fine.
If you have determined that the cable is not the issue, then you may want to consider trying a replacement battery as depending on the length of time you have had this camera for, and the conditions in which the battery has been kept (for example, left in a cold car on an icy night), it can weaken the charge hold within the battery and ultimately at some point mean that there's not enough charge held to power your device.
You can get a cheap replacement battery online (for example Amazon).
Finally, you could get a mains adapter charger for your camera, so that you are getting the best power to your camera, and a more convenient way to charge your camera in the future.
I would recommend trying a replacement battery first as not only is this the cheaper alternative, even if you discover that it wasn't the battery, and your original was fine, then it's very handy to have 2 batteries so that you can charge them both and if one battery happens to run out in the middle of taking some shots, you are prepared :)
Here is a helpful Amazon link so you can see the various batteries you could get for your camera:
These results show quite a few different replacement batteries, all at varying prices (the cheapest will be fine (£2.76))!
Also within these results, you can see the mains battery charger that I also mentioned.
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All the best,