Whether you use this information to retrieve files after windows locks up or to access your computer without having to purchase a new CD from Windows, I suggest researching the laws concerning these types of activities before attempting them. I do not support piracy but I do believe users should have access to Windows, i.e. their personal files even in the event of an invalid/used product key.
Step 1: Step 1 - Login to your Account and access Explorer
Turn on your computer and login to your account. You get a message telling you that you need to activate your product, Click Yes and the Activate Windows screen will load. Now press the windows key + U and Microsoft Narrator should pop up. Click OK for the little disclaimer Narrator gives you and behind it will be the Narrator option screen. In the top left of the Narrator option screen, you'll see a little computer icon, click it and a drop-down menu will appear. Click on About Narrator. On the next pop-up, click the link Microsoft Web site. You now have access to Internet Explorer!!! Whether you have an internet connection at the time or not, it doesn't matter, we aren't actually trying to get online.
Now we are going to access your desktop and Start bar. In the address bar, type: C:\WINDOWS\explorer.exe and press enter.
VOILA! You have access to your entire computer just like you normally would! Don't close Narrator though, because windows tends to realize what you're doing and reset back to the Activation screen. It's not bullet-proof, sometimes my computer will reset back to the activation screen, but you can just do the same thing again as many times as you want!