clean win 7 install while keeping old win 7 serial

[noid4u]

im giving my PC to a friend but i want to clean windows to a fresh state. however i only have an illegal copy of win 7 and cant find my original win 7 key. is there a way to retain the current win 7 key and still be able to do a clean install or anything kinda similar?

 

[noid4u]

well i just found out i can go into control panel>sytem and security>system and look way down of the tab and my serial right there. derp