2006 Prius won't start, battery dead?

I tried to help jump-start someone else's car the other day, with the result that my 2006 Prius also died. Someone else jump-started my car, but for the next few days it was being weird and a couple of times gave me the "P lock is abnormal park on a flat surface and fully engage parking brake" error. I can't remember exactly what I did, just fiddled with it until it would go.

Then the other day, as I got out of my car and pulled the key fob out of the key slot (the fob's battery has been dead, but I replaced it the other day), all the lights went dead on the dash. I had other things to do, so I moved along, but when I came back to drive it the next day, everything was still dead in the car, not even a single light on in the dash. It doesn't respond to anything I do. I've tried jump-starting it several times, but no dice. I bought it used 6 months ago and the guy I bought it from said they had replaced the hybrid battery with a Toyota battery only a year or so before...

Any help would be appreciated, thanks!