Plug in the device that is not being detected. Go to your device manager. Delete everything under Universal Serial Bus Controllers. Then, at the top of the Device Manager, click on action, scan for new hardware changes (that may not be the exact wording, but it's close). The computer should re-install all of the root hubs and controllers. At this point, it should also detect the drive or dongle you inserted.
Sometimes, a USB device sort of "takes over." Almost like it doesn't want to share the USB ports with anything else. Don't know why, but the above has always worked for me.
I also have a firewire port, and a camera with a loose connection. If the cable becomes loose and looses connectivity, then regains it, the firewire port stops functioning, and I have to delete it from device manager and reinstall it. Need to get the camera fixed.