If you have followed Jeff's advice, that should restore your USB drivers and the connection.
Next step, open Windows Control Panel / Device Manager / System.
USB is usually the last entry. Check that all the drivers are correctly installed and are not showing the ! alert. If something is, delete it and restart your computer.
If that does not work, you may have a hardware failure. I did, it was a head scratcher figuring that out, everything looked fine in the control panel, but no connect.