What are your symptoms?
The problem I've seen the most is that a pin gets bent, and if it is touching another pin you can get messages about a USB port power surge or something like that. Turn the PC off, shine a good light in there and if the pins aren't all straight, use a tweezer or a straightened paper clip to straighten them.
Other than that, make sure the USB device or cable isn't bad. Does it work on another computer? Do you have other devices and cables to try? Chances are all of them aren't bad, but it sure is nice to see them working somewhere else so you can be sure you've isolated the problem.
Next I'd probably go through the control panel and see if there are any trouble shooting steps or software repair or reset that can be done, but I'm pretty doubtful you'll find something useful. That'd be my last gasp before paying for service.
I've never had a USB port go bad ,though I do have a Dell laptop that had a port that was always tough to plugh a cable into, and one day the port connector came out with the cable. I couldn't reattach it. Dell wanted me to send in the whole laptop, I didn't want to do that, so I just got a USB hub for when I need to use more than one port.
I don't know what it takes to fix a USB port if it's actually gone bad.