Saw the ad for Registry Mechanic on the main page of another large computer forum (is that what's being advertised on this Forum also!?), thought it should be a good idea to have that as it was advertised on the forum and therefore obviously approved, and highly rated by PCWorld. Downloaded it, paid for it, installed it and ran it. Then computer restarted and it required my product code to start Windows. Typed in product code, but says it's invalid. I called MS Support, they first gave me 2 different product codes to try to unlock Windows, neither worked. Then transferred to a Tech who said I had gotten a worm with Registry Mechanic which was the reason I was unable to access Windows. They worked with me for over 2 hours, including going back to and installing a backup registry created the day before this Registry Mechanic was installed, but I am still being blocked from starting Windows. They are going to work with me more tomorrow. Further, the Tech said emphatically that such tools should not be used on the registry, that it would only lead to problems, even without such a worm. A MOST unhappy experience from what should have been a trustworthy source!