Can't type in password when logging in

I called support and got a fix that helped: Turn your computer completely off. Next, locate the "Command" "Option" "P" and "R" keys. Be prepared to hold them down once you've turned on your mac. Turn on your mac and firmly hold down these four keys. You will hear the mac chime once. Keep holding the keys. You will hear the mac chime a second time. Release the keys. You may hear a third chime, or you may not. Either way, once the system resumes operation, the keyboard may be recognized once again.

The rep I talked to told me we were "zapping the PRAM". I found more about this process here: What does Command + Option + P + R actually do?

Non-Apple "anti-virus" garbage has been known to cause that problem. If you installed anything in that category, uninstall it according to its instructions.

Yes.

Because Kapersky ((sic) it’s Kaspersky) is not working correctly with Sierra.

Are you using an apple brand keyboard? Since updating to 10.12.2, my apple brand keyboard is non-functional. I now have to use an old bluetooth microsoft keyboard, because I can't seem to get my apple keyboard to function.

Why was everything fine before i updated to sierra?

Like all similarly categorized junk, "Kaspersky" has been, and always will be, 100% worthless on a Mac.

And, like every macOS developer big and small, "Kaspersky" has had the better part of a year to update their products for Sierra compatibility. How well do you suppose a product designed to "protect" your Mac from (generally, imaginary) threats would respond to a real threat, one that was not provided to developers worldwide for evaluation purposes, one presumably designed to be difficult to detect and eradicate?

You decide.

The vast majority of Mac problems reported on this site are the direct result of using garbage products just like it. They are the threat they claim to prevent. Read Effective defenses against malware and other threats.