[Reeyal]

Windows activation is based on the machine code. The machine code is derived from motherboard ID, hard drive ID, and CPU ID. If any of those IDs change, Windows thinks you have a new system. By the way, retail Windows usually gives you 2 activation; however, legal you can only activate 1 computer.

At work, one of my many tasks is to look after 350+ PCs. I have shuffled many computer components around, and most of the time, they didn't require an OS reinstall. Of course, I went from similar hardware to similar hardware. The only time I needed to reinstall the OS was going from and to dissimilar motherboard chipset.

To be technical, what prevents the OS from booting is the boot manager unable to read the hard drive. The first thing the boot manager will load is the hard drive drivers; IDE, AHCI, or RAID. If those drivers change drastically, the OS won't load and gives you a blue screen or "unable to read boot device" error.

To answer your questions above, take an Acronis Backup version 11 or above of hard drives. Now, restore all of those backups to their new hard drives. During the Acronis restore, there is an option to keep machine ID from the backup image. If you're changing just the hard drive, Windows shouldn't ask you to activate.