Priv won't accept my lock screen password or 'blackberry' to open

My Priv has a user password enabled for the lock screen.
Normally I enter the password and the system opens to the home screen just fine.

However it now prompts me to Enter "blackberry"

I've tried entering "blackberry" without the quotes and it does not unlock and display the home screen, nor does it provide a prompt for my normal password.

I've powered the Priv off multiple times, removed the SIM and SD card, drained the battery and then recharged it -- all with the same results.

Last I checked earlier this week, the Priv had used up about 50% of the internal memory so it's unlikely that it's experiencing anything close to a 'boundary' condition in that regards.

Any suggestions on how to proceed from here. I really need to ensure that I have a complete backup of the data on the phone (last one was too long ago to consider it to be useful today).

Thanks for any help.

NM.
I completely drained the battery once again. left it uncharged for several hours, then recharged it and I was able to get a normal login prompt and was able to get into the phone ok.