Pontiac Grand Am weird electrical problem?

A few months after I bought my car it started to act funny. The dash lights would go from normal to dim and then in a split second turn off and back on. My head lights would dim and shut off and back on ( but not always when dash lights did). My radio would shut off and back on every 3-5 seconds. But would always go back to the same radio station or cd. I thought it was my alltinater. I had it test and it wasn't it. My battery is brand new and has new connections as well. Then I had a new issue. This has happened 5-6 times now since June. While drive my car has died and will crank but not start. When it does this the inside of the car has now power. My headlights dont come one I can lock the doors, roll down the windows, pop the trunk, no heat or air works. Also my key gets stuck in the ignition. Can turn it to try and start the car and turn it all the way back but it wont come out. If you do get it out and put it back in again it gets stuck again. I have even let the car sit for 12-14 hrs and it would still be dead. One time when it died my grandpa came to tow the car the car. When we pushed it on to the dully (but didnt go up) it hit it hard enough twice and the car started and had no issues for a few months with it dying but still have the dash issue and radio/head light issue. Time before if my son who is 5 jumped up and down on the truck would get power to the inside and then lose it. I am honestly lost at what is going on with the car. Is this a ground wire issue. If so how can I track it down. Or find out what is causing this.