Do you have other USB devices working on your computer? If not, it is possible that the BIOS settings got reset to the default, which for many older PCs was to disable the USB connection.

To check that, most common BIOS (AMI and some others) will tell you to press F2 during startup. This will take you through the BIOS screens. Find the USB-related entries, and make sure the connection is turned on.

Good luck