Flashing red dot on dash, car will not turn over

Hi,

I had the heater core on my vehicle replaced a couple of weeks ago. Ever since it had issues with turning on. It would turn on for 5 seconds then turn itself off. It would take multiple attempts to get it to stay on. Every time this happened the red light on my dash would flash.

Last night the same thing was happening while I was at school, except I couldn’t get it to stay on. A classmate tried to help, he put the car on reverse as soon as he got it to turn, but it shut off again. Now the car won’t even turn the red dot is still on the dash. Any ideas on what this could be?

My radio, heat and lights are all working. It’s definitely not the battery.