Prius Red Triangle of Death

2007 Toyota Prius 210,000 ish miles So.. this happens sometimes when I try to start my car. I can usually hook up the jump pack and push the button a few times until I get the little 'beep beep' Ready light. Triangle goes away and I go about my business. Actually before this moment there are no lights except the actual Check Engine light (not Maint. Req. which is always on) then I can usually use the jump pack. Tonight though it wasn't doing it.. we actually hooked it up to my FIL's Jeep and it just would not freaking start. I was just about to give up and let it roll down the driveway to a flat area so I could do the flat area thing it wants me to do. Although I never actually had to do it before to get it to start. Like I said, usually I just gotta give 'er a little more juice and eventually it'll go.. Also, I think it's worth mentioning cause it was freaking me the F out -- I was parked in an uphill driveway and it was ROLLING BACKWARDS WHILE IN PARK. Unless I applied the brake or the E brake. Idk but that seems significant. Anyways, I was gonna roll it back to a flat surface and apply the E brake and all that, but we had to hook it back up to the Jeep for a sec so I could put it into neutral. And it just.. started. Then I drove it the 75 miles on the highway back home. EDIT: to add that if there's someone out there that's an actual expert on beat up Priuses(sp?) DM me fr. I could go for days about all the weird shit this car does. And the sounds it makes.