With most new motherboards, onboard USB power supply (the one you damaged, power is separate from USB data interface) are indirectly connected to the hub, usually in series with a resettable PTC fuse, depending on onboard voltage regulator, 12v in parallel with 5v might clamp at the regulator and drop resistance which increases load on the fuse enough to cutoff, tho not continuously as this type of fuse resets when under minimum current threshold which may have triggered many times and left damage in the end.( would have still worked if the process was done in short time) What you can do to determine and workaround the issue: -Get a USB Hub, a 5v phone charger, and a male to male USB cable. -Plug the male side USB hub to the dead port. -Plug the male-male USB cable end to the phone charger, the other end to the USB hub. -Plug a flashdrive to test, if it work then the logic board needs repair. (Usually not complex and not worth to replace the entire board as it's relatively simple procedure in most repair...