In your case, despite there being no clear why it would happen, you might try to swap in a new one..
There's also a chance that an updated motherboard/chipset driver could repair the USB port problem.. Are other devices having issues with the USB ports? Have you checked the wireless adapter's website to see if there are NEW drivers for the device.?
Hope this helps.
i recently moved my desktop computer to another room and when i boot up it wouldent find the linksys usb dongle (wusbf54g)i tried every thing reinstaling drivers, trying different ports, restoring to a previous date. whenever i plug it in it says "usb Device not reconised"