2005 Prius Honks Constantly After Hitting Unlock On Key Fob & More

I recently replaced the 12v battery in my 2005 Prius after discovering that the old battery was only supplying 9v and the car wouldn't start! About 1 month later, when trying to start the car, the dashboard acted strangely. The fuel gauge was flash back and forth between 1 bar and full bars and the gear symbols would flash at seemingly regular intervals. I replaced the key fob battery and that solved the problem.

Now cut to 5 days later, I try to unlock the doors with the key fob... and the horn started honking a struggling muffled version of the normal alarm. Only the driver's door unlocked but you could hear a rhythmic clicking coming from the locks inside. It sounded like they were trying to unlock but couldn't. I couldn't start the car or stop the honking and lock clicking, so I removed the horn's fuse. It has since stopped honking and clicking, but it will not start.

Can anyone please help me?