If more diagnosing is needed... these are less likely since it would have had to have a failure just at the time that you were working with it, so its possible but unlikely to happen. Still, it's relatively easy to diagnose and isolate other possible causes.
If you have another quad you can test with... plug in another quad and see if it works as expected. If it does, the problem is with the quad in question. If the problem also happens with another quad, then the problem may be the USB port on the computer or the USB cable.
To check if the USB port is at fault, just plug into a different known working USB port.
To check the USB cable, again, just use another cable to test with. Please note there are two types of USB cables that exist. The standard one supports both data and power... and the ones made just for charging only supports power. So make sure to use one that supports data also.
The last place to check... is some type of failure on the computer you were using which could be a hardware or software caused issue. The easy way to check for this is using another computer to see if things work properly or not. I won't go into diagnosing the computer if that's the problem since that requires a lot of other steps.