No USB Root Hub

Husband had problem with a USB device that makes his CAD work, so somehow managed to delete all the USB stuff. I have, updated drivers, uninstalled all the big yellow question mark items, restarted computer, still cannot find drivers. I have cleaned the computer out, unpluged the cables, including the power, still comes back on with big yellow marks by the unknown devices. Looks like there is a lot of stepping on IRQ’s going on but with Windows XP I don’t think that is a problem. The thing I think we are missing is called a USB Root Hub. Any suggestions would be greatly appreciated.