If you have never installed SP 1 onto your version of Windows 7 then you will need to perform the in place upgrade / repair with installation media without the Service Pack integrated into it.
You should be able to acquire the ISO from here Link Removed
Please make sure that you obtain the correct version and bit architecture (32 or 64) that's identical to your current installation.
Burn the ISO to a DVD and you should be able to perform the in place upgrade / repair as per my earlier link.
Good luck and keep us posted