Ok so i just recently got all the parts for my new gaming pc but forgot to purchase a copy of windows 7 for it. I have my old 250gb hard drive that i kept for safe keeping and stuff so i was wondering if i take my old hard drive out and put in into my new gaming pc... When i boot it up when im all done building it, will the boot system recognize that i already have windows 7? Or will i have to purchase a new copy of windows 7?