I had a hard drive fail on a netbook, and I put in a drive from another of the same brand that had died for other reasons. The new drive took like fish to water - no blue screens, etc. And Windows even updated, as did MSE.
But I'd like to make this machine honest by entering the Windows 7 product key that's associated with the motherboard, so the next owner will never have a problem. Will I have a problem doing that? I don't want to lose what I already have.