I was reinstalling Windows 7 after wiping the hard drive. It kept telling me I had an invalid product code even though I was entering it in off the original box I had purchased it in. Turns our I was doing a fresh install of an upgrade version of 7. Microsoft wants the old version on the computer to work. See this link:
Microsoft:
http://windows.microsoft.com/en-US/windows7/Windows-7-activation-error-invalid-product-key
So I found these instructions below. I used option 2 and it worked like a champ.
Other:
http://winsupersite.com/article/windows-7/clean-install-windows-7-with-upgrade-media-128512