I have an acer aspire 5732z had windows 7 home with fried hard drive, (never bothered to get replacement as i didnt have disks) anyway I also have an HP laptop with a fried mobo due to heat sink overheat with a good hard drive also windows 7 home operating system, what do i need in order to get windows 7 operating system to run correctly again? do i need a new windows 7 retail disk with a new COA??? Can I use my old COA ???