OK, I think I did something bad. I'll explain what I did & saw, and hopefully someone can fill in the blanks.

My car: 2003 V8, battery is 1 month old

My neighborfriend knocked on the door, asking if I could give her VW TDI a jump start. I tried my little jumpstart box, but it didn't have enough power, so I drove over and got out the jumper cables. Kicking myself because part of the reason I bought the jumpstart box was so this kind of thing WOULDN'T happen.

She said that she left her interior light on all night, so the battery was completely dead. After idling while connected, hers started. Drove back to my driveway, everything seemed normal. When I shut the engine off, I heard a muffled "pmmph" noise from the subwoofer, like a cardboard box had fallen over in the back so I didn't pay attention to it. But when I hit the remote to lock it, nothing happened.

Got back in to start it back up, and it was like there was no battery connected. Total dead. Went inside to get my tester and charger. Battery tests completely fine & full. For whatever reason turned the key to "on" again, and it was acting normal. Chimes, etc. So I thought maybe there was a thermal circuit breaker, and the jumpstart with glow plugs and such pulled too much power. Turned the key a little more to "start" and it went completely dead again -- gauge needles froze in place.

I'm going to do some searching and looking once I'm able, but are there any known things I should check first?

Right now I'm looking to find a "main fuse" or circuit breaker.