Your motherboard might be on the way out man, save yourself the trouble and find a replacement, one of my cousins pc's motherboard started failing when USB ports started being " Not recognized" but I disabled the port and kept the motherboard alive a little longer...however then a capacitor blew and it leaked all over the internals, frying the thing and everything in it, somehow the hdd ended up corrupted, probably due to a short, he lost everything.
I would not take chances, just buy a new motherboard and save yourself the trouble.