Some USB ports may look like they're not working because of corrupted drivers. A number of (front panel) USB ports on my kid's old Vista PC quit working after she repeatedly yanked out a USB device instead of properly ejecting it. Device Manager showed all USB ports were working. But, some simply won't open a USB device.

After I did an OS reinstall, the front USB ports worked again. The only way to really know which USB ports were bad was to plug in a USB device and see what happens.