Disable USB Devices:

Disabling USB ports can be a smart idea to add security to the computer. This can be really handy if the computer is on a public place where the chances of virus and other malware infection is really high. You can easily disable access to USB ports with the following registry hack:

1. Open the Registry Editor (Start -> Run -> Type regedit and hit Enter)

2. In the registry, navigate to the following key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor

3. In the right-side pane, double-click on “Start”.

4. In the “Value data” field enter 4 and click on “OK”.

5. Close the Registry Editor and reboot.

To enable USB devices, follow the same procedure as above except in the step-4 enter 3 in the “Value data” field.
Works on Windows XP, Vista and 7.