I didn't even know that microsoft is not selling Keys for home use, well, now i know. So if someone want's to sell me some microsoft software, what do i have to check to make sure it's ''legal'' and ok?
Do you have a certificate of authenticity? Or did you buy your laptop from an OEM provider. OEM providers sometimes embed the license key into the computer's BIOS. You should have the restore CDs which say that on a laptop.
If you have a desktop and no certificate of authenticity, even if your license activates and seems okay, it's still considered invalid.
http://www.microsoft.com/OEM/en/licensing/antipiracy/Pages/COA_hologram.aspx#fbid=zipZ8l7kzZS