My roommate and I were installing a new motherboard, processor, and hard drive in my computer. When trying to reinstall Windows Xp pro on my new hard drive, and found that I can't find the product key for it. I tried to reboot the computer with my old hard drive (that had windows on it) but it said it was a missing a certain file (<windows root> \system32.hall.dll) and couldn't boot up. I do have another product key that I could use, but it is for an unopened OEM disc. Could I use that product key temporarily to boot it up until I find the original?