My laptop says that my copy of Windows 7 is not genuine, I know that it is, any help appreciated?

I have had this Lenovo laptop for almost 18 months. It came directly from the manufacturers with Windows 7 already installed on it. I have never had any problems with Windows on it before but tonight when I turned it on after I had inadvertently left it with a dead battery for about 12 hours or so, it came up saying that my copy of Windows is not genuine. After following the suggested links I was about to type in the product key from the sticker underneath the laptop but I just wanted to know whether doing this will clear programs and personal files etc from the laptop.

I would really appreciate any help with this. As it is nearly midnight, I cannot access Lenovo's technical department but having been away on holiday for a week I have a lot to catch up on overnight and need to use the laptop to do so, but I don't want to do this if there is a problem with my Windows, especially as I had a pop up notification saying that I may have been a victim of fraudulent software (although I don't see how this can have happened). I have downloaded and run the Windows verification tool and it still says that the copy is not genuine.

Many thanks in advance

Kate

xx