i just finished building a new computer the other day, the only thing i used from my old computer was the hard drive, when i go to run mynew machine windows runs, but when i log in it says you must activate this copy of windows. when ihit yes it goes past the log in screen and a window pops up and says "this copy of windows is already activated" i hit ok and it just logs me out. it workedfine on mylast machine. am i just screwed and have to buy a new copy of windows or can i reformat and reenter the product key that came with my oldcomp?