Windows 7 - Read only external hard disk or USB

Open regedit and go to

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies\WriteProtect

1	HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies\WriteProtect

If the key exists change the value from 1 to 0

Then reboot