W7 Best Option

I bought a used M2010 on ebay. It has dual boots from two drives, one Vista ultimate with key on laptop. The larger drive has oem W7 ultimate. Everything was fine, activated well and was receiving updates. About a month ago the video card crashed/died and I had it re flowed..I get it back and it boots up with the date returned to 2007 and the W7 drive has black screen with something about not being a valid copy. I reset the date, reboot and come back saying it needs activating..I entered the key(had it from Belarc copy) but it says it's not valid. I definitely like the W7 better with the aero peek and larger task bar for my eyes. So what is my most inexpensive next step ? I am curious as to how this was loaded and continually working before the video problems? Since it's already loaded can I just buy a valid key?

Thanks. GBY

I believe you could buy a valid key and insert it as you would normally, but since it sounds like a pirated copy from eBay, I would probably want to wipe the drive clean and do a fresh install on my own, out of peace of mind.

Hi, Thanks for response. I don't think it's pirated as it says it's Dell OEM.