Question regarding windows 7,had to reinstall but cant find my product key to activate please help?

I had to completley wipe my system clean and start over cause it crashed but, the sticker on my laptop containing the product key for activation wore off and i can no longer read the letters/numbers. My computer is no longer under warranty and i really dont want to spend another 200 bux for a copy of windows 7, is their anywhere in my computer I can find or get this information?