You will have to problably reactivate thru phone. It happened to me with Office 2013.
You moved a HDD from one PC to another and it worked? Seems strange.
Sysprep is avaliable for this.
Besides that, I dont know, leftover files/drivers/etc. from your old PC hardware is something I wouldnt want left behind.
Yup, moved from E8400 Core 2 Duo to an i5 4670; new motherboard, RAM, GPU everything. Worked flawless. Apparently, Windows 7 can do it as well, but I've never tried it on that. All I did after was run the install disc that came with my new mobo, to make sure it had the right drivers. Leaving old drivers on Windows really isn't a problem considering a huge part of a Windows install is 1000's of drivers you'll never ever use.
Saved me a crapton of work, that did.
Admittedly, I was pretty gobsmacked that it worked; I fully expected it to BSOD on boot and had a USB stick all prepped and ready to go for reinstalling.