2012 Prius Lock Theft Light Engaged

How do I fix? Tried both key fobs still can't unlock theft mode Why did it get into theft mode? Driving and stopping doing errands noticed I couldn't lock car. Got only one beep not two beeps when locking?? Started doing one bee p locking when my husband uses other key fob for 2 weeks? Now car won't start. Battery isn't dead can turn on lights inside and outside of car but see fast blink top right of screen??