Anti theft system prevent vehicle from starting

I locked the back hatch up earlier in the morning and I was gone all day. When I got back I went to get my tools out and my key had came apart in the morning and I did not notice, I snapped them back together unlocked it and noticed the dome light flashed I did not think anything of it. I got things out of the back and put a new exhaust pipes and muffler on and when I finished I went to start it the dome light flashed and it would not start. I would like to get it started or by pass it.