You would need a Win 7 install disk that included SP1 of the same architecture (32 0r 64bit) as you have installed and then you can perform a repair install.
When prompted for the product key, if using an OEM machine then use what is on the COA sticker.
http://www.sevenforums.com/tutorials/3413-repair-install.htmlThis link may work for you but when I've tried it, it isn't responding but may do later.
As advised, back up your drivers folders first onto something like an USB stick and then you can drop them back in after the repair.
The three folders can be found at C:\Windows\System32
