My pc had a virus so i found a windows 7 32bit professional cd that I presumed was 64 bit, bad mistake. It was 32 bit and i installed over the original 64bit home premium I had on my system. Can i get the 64 bit back? my pc was a present so i dont have the original cd for the os but theres a sticker on the side with the original product key for the 64bit os.