I will be changing motherboard and processor, and was wondering if I will need a fresh clean OS install or not if so I need to do some backing up some data. Thanks!
If it was not the same as the other installed. You may have to. I would try a repair install first. Make sure you make up a backup of the current drive. Otherwise you could end up losing valuable data.
I recommend reinstalling it from scratch. Even if the repair install works there will still be remains of drivers etc. on your system. If you upgrade your CPU - mainboard combination that's always an occasion to reinstall the OS and benefit from a fresh system with no legacy problems.
Windows 8 is more forgiving than the previous versions of Windows and the answer is YES, you can put in the HD with your current Windows and it should work. There's no repair install. Windows will start off with the message: Getting devices ready then will install the new drivers for the new MB. The advantage is you will have all your data and installed applications available. However, as a precaution, Use: Macrium Reflect Free to backup your Windows C: Drive first then:
Make sure you set the BIOS to be the same style as was in the old MB ( MBR or GPT)
Make sure you have the internet cable connected so Windows can download and install the new drivers.
After booting up Windows in the new MB, you'll need to re-activate your Windows again.
Go to Device Manager->View->Hidden devices and uninstall all the grayed out drivers.
