Why does my iphone not charge from the computer?

I posted a previous post on "why does my iphone not charge" and people wanting to act smart saying "the phone died" and bla bla bla (aka stupid answers) to try to look smart, but its charging GREAT from only the outlet, may someone respond with a legit answer and not something that we all already know could be possible (no one told me to plug it into the outlet, it was a recommendation by a friend) but why did it once charge great from the USB pc port, after that one charge (its first charge by me) i left its airplane mode off (first time having a iphone) so it drained the battery all the way that it wouldnt let me use it before charging it, but after the one successful charge it no longer wanted to be charged from the computer (until the recommendation came) so now I only charge it from the outlet, how come? Its a (bought used) 3gs iphone, Please ONLY LEGIT ANSWERS

Probably the UBS port itself. May not have enough power going to it to charge,; just enough to recognise. If it is a desktop computer try a USB port in the back.

You probably need to install the driver needed to charge it

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