If you're logged in as an administrator and that option is still disabled, it could be an issue with the install.
Click Start > All Programs > Accessories > Right Click "Command Prompt" and select "Run as Administrator"
In the command prompt type
Let that run, restart and try again.
Click Start > All Programs > Accessories > Right Click "Command Prompt" and select "Run as Administrator"
In the command prompt type
Code:
sfc /scannow
Let that run, restart and try again.