I presume you've tried other hardware in the USB ports.... printer, card reader, light, flash card etc.? If all the ports are dead do they show up in your Device Manager? [XP - rightclick "My Computer/Manage and click the Device Manager in the Computer Management window that pops up].
If nothing, try downloading a USB driver for your operating system.
Has the plug for the USB ports come away from the motherboard? There are usually 2+ USB sockets on motherboards, try putting the plug on another one.
You can get a small converter plug that takes a USB plug and goes into the mouse ps/2 socket on the computer, that will at least enable you to use the mouse while you look for remedies for the USB ports.