[Blu Vivo IV] Phone prompts reboot at startup

Hello there!!

I have purchased a BLU Vivo IV a month ago. About a week ago, I installed an update of the OS. Right after that, every time I turn my phone on, a message pops up with a beep, saying:

Power Off

Long press power key and volume dowwn key for 8 secods to reboot the phone

It gives me the option to "dismiss" or "snooze".

Doing what the message suggests just turns off the phone. After I boot it up, the message appears again.

This phone is also having an issue with its battery: the power usage breakdown shows that the Android System consumes 70-99% of the power. I can make normal usage of the phone (music, messaging, Internet, some rare calls) for 12-15 hours on its battery.

Any insights? Has anyone has the same problem with this device?

Any help is greatly appreciated!