The next time this pops up, click to follow the prompt and go onto to reactivate the computer.
I tried this, but the popup still persists. I think the 3004394 update permanently corrupted one or more of my system files. Interestingly, a system restore for 12/10/14 did not work (after rebooting, a window told me the system restore failed with an unknown
error.) But another restore point on 12/7/14 worked.
I'm keeping my fingers crossed, hoping that the Genuine Windows Notification will go away, now that I managed to do a system restore.
After I did some reading on other websites, I think I will stop downloading/installing updates labeled "Update for Windows 7". After all, the security updates are far more important, and they seem to be less likely to corrupt my system.
Thanks for the Christmas present, Microsoft!