I just build another new computer and installed windows Xp home edition onto it. When i went to activate it the Product key will not work. I have activated this particular copy of windows on 3 systems with no trouble this far. So, i did some research on google and found out that i should not have been able to do what i did (activate on 3 systems with the same disk) and that i cant activate it on this system. My question is do i have to buy another copy of windows just to activate it?