I was given a Windows 7 computer and the hardware was dead but the 500 gig HD and 4 gig of ram were fine. The HD was filled with viruses but that can be fixed. I loaded WinKeyFinder (http://www.winkeyfinder.com/) and it told me the serial number. I had another computer with Vista on it and so I put the 4 gig of Ram in that machine and got out my generic Win 7 install disk and wiped the drive (it had no viruses) to be safe. I put the install disk in, installed, and it accepted the serial number from the dead machine and registered with Microsoft. Now to wipe the 500 Gig drive with the viruses and use it as an external drive.
Great little piece of software. I have recovered XP, Vista, and Win7 serial numbers. Why not look on the sticker? The Vista, later XP, and WIn 7 stickers wear off and become unreadable. Now I have a really nice machine to use for timing.
What if WinKeyFinder has a Trojan on it? Who cares as I got the serial number back and did a fresh install.