As usual, the normal warnings about using regedit apply. If you use regedit incorrectly you may cause your system to fail to boot.
1. Run Regedit
2. Locate HKLM\system\currentcontrolset\control
3. Right mouse click on Control and select New Key
4. Enter the new key names = StorageDevicePolicies
5. Right mouse click StorageDevicePolicies, select New then DWORD
6. Enter value WriteProtect
7. Set this value to 1 to allow USB drives to be read only or 0 to allow normal USB operation.