Any hardware change to the system, network card, hard drive, processor upgrade, video card upgrade can trigger a reactivation. It's been that way for ages.

They base the activation on some combination of unique indntifiers of your hardware, change enough of it and it thinks you are using it on a different machine.

Sucks to be sure, but it's been that way for a while. You could have made up a name and probably cut an hour off the phone call.