enable and Disable usb by regedit

  here is the simply way to block USB port try this,..................

To disable the access to USB port, in windows XP and 2000:
1. Click Start, and then click Run.
2. In the Open box, type regedit, and then click OK.
3. Locate, and then click the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor
4. In the right pane, double-click Start.
5. In the Value data box, type 4, click Hexadecimal (if it is not already selected), and then click OK.
6. Quit Registry Editor.

To re-enable a disabled port:

1. Click Start, and then click Run.
2. In the Open box, type regedit, and then click OK.
3. Locate, and then click the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsbStor
4. In the right pane, double-click Start.
5. In the Value data box, type 3, click Hexadecimal (if it is not already selected), and then click OK.
6. Quit Registry Editor.