HELP! Electrical gone crazy!

This morning I tried starting my 05 Prius to go to work and everything went on lights, horn, hazards, like a panic button was hit - navigation didn't turn on. I shut the car off and turned in back on. Now, half the electrical turns on - clock time is very dim, and I hear a clicking noise constantly. The power button is amber and the park green. To turn it off, I have to hit the park button though it doesn't look like it's doing anything and then hold the power until it goes off. Even when the car is off the door ajar light and beeping goes off when the door is open.

I checked the fuses under the hood and on the instrument panel. Nothing looks bad. Is the battery almost dead?

By the way, the gas engine never kicks in, and on the display there's no box around any "gear" - park, drive, neutral, etc.

 

No headlights will turn on. The wipers move at 1/4 the normal speed. The fog lights turned on doesn't turn on the lights but makes the electrical seizure and making a clicking noise - after that everything blinks - gas meter, drive letters, warnings signs.

Oh, and it's the coldest day here so far for winter - 18F, all other days have been at least in the 30s.

 

Whew thanks, even if it turns out it's not - it's a very cheap test and much better than my other option - have it towed for about $100 and looked at for about $150 before they even do any work. With others cars I'll always noticed it's the battery by the way the car starts up, but with the Prius it doesn't start up the same.