On the PC I described above I have added and removed several additional hard drives over the years as I expand and they die. Recently I had my old Nvidia graphics card die and replaced it with an ATI.

I uninstalled the nvidia drivers then installed the ATI ones and it seems to work fine. No activation complaints.

It's actually been very easy to keep this thing running. Pretty much just plug in new parts when old ones fail. I think my spinning rust HDD is about to die though so I should take the suggestions in this thread and go through the process of moving the OS to the SSD.

At some point in the distant past I might have replaced a Core 2 Duo for a Core 2 Quad. Or I may have built it this way, not sure.

When I've done this, on first boot Windows detects the changed hardware and there's a little mini-installation screen that says "Reconfiguring Hardware" or something. Things seem to work afterwards. Changing the Motherboard may cause activation issues on OEM licenses. Changing from Nvidia GPUs to other manufacturers may require e.g. DDU to remove their drivers completely.

Yes, first "deinstall" HAL, then reboot.

Then deinstall all your cpu's (if the number of cores changed), thats no joke...deinstall your cpu's (all of them), then reboot.

Update all the drivers...that's it.

It won't break. Activation may or may not whine at you, and if it does whine it might resolve itself after a couple days.