Re: galaxy tab 3 won't charge when connected to pc
If it charges using the wall charger, I'd bet on Belodion's answer.
If it doesn't charge on anything, it's either a bad USB cable or the microUSB connector in the phone lost connection on one of its charging pins. (You can't fix that yourself, the phone has to be opened and the connector has to be resoldered.) It's also possible that the charging circuit in the phone went bad (although that's very rare). And it could be a bad battery. If you don't have another battery to try out, bring the phone into your carrier's store and see if they have an S3 battery they can pop into your phone for a minute to see if that, or a different USB cable, fixes the problem.