This was recently posted on another site, by a colleague. I think it is worth repeating verbatim
""Over recent days, there has been an increase in reports of blue screens and startup malfunction. I made a reference to this problem some time ago, but, as a reminder, this is worthwhile reading.
There has been a sudden spate of BSOD's over recent days. It could be associated with these two items from Microsoft's pages.
"Validation helps confirm that a copy of Windows Vista is activated and properly licensed. Users may be asked to validate their copy of Windows when they download content that is reserved for users of genuine Windows from the Microsoft Download Center. Validation can also occur as part of an update from Windows Update. In some instances, a computer that has previously passed validation may fail the validation process. This may happen because Microsoft constantly discovers new forms of piracy. As new forms of piracy are discovered, Microsoft updates the anti-piracy components to help disable the emerging threats and therefore, a copy of Windows that previously passed validation may fail a later validation check. Copies of Windows Vista that are unable to validate as genuine may need to activate and validate again in order to maintain full functionality. "
From the same page, if you feel you have been deceievd into the purchase of a doubtful genune copy:
"If your copy of Windows is not genuine, Microsoft can help you to quickly fix the problem and get genuine. Customers can contact Microsoft Support or visit the Microsoft Genuine Advantage support page to resolve the problem. Microsoft also offers several options to help victims of counterfeit software obtain a legal copy of Windows, including a complimentary offer for victims who were deceived into buying high-quality counterfeit copies. Read the Frequently Asked Questions to learn more about genuine Windows offers. "
The portion I have "bolded" refers to this link. Well worth reading.
Whilst I would emphasise that I do not, in any way, support pirating. If you feel you may have a less than genuine copy of Windows, one solution is to turn off updates. ""