Q: If I replace the motherboard and processor in my desktop (PC), but I use the same hard drive, will my version of Windows still work?
A: At boot time with the new MB, Windows will ask you for the installation CD because of the new hardware. It is mandatory to reinstall Windows. If you continue to use the old installed Windows setup, you will end up with a lot of drivers from the old motherboard mixed with the new ones. This is crappy. Make a backup of your files BEFORE the MB swap. Also, there is a chance that the old hard disk geometry (the BIOS setup) would not be recognized by the new MB. Maybe, you should consider to buy a new hard disk, too, and to make an all-clean Windows install, and using the old hard disk as a slave, instead. Not matter what you do, you need to re-activate Windows. This is not a problem. P.S. Not all motherboards are "the same". The memory and/or CPU that works in one MB not necessarily will work if you "transplant" them to other MB. You are warned!