Imac 2014 24 inch keeps rebooting

My IMac keepsrebooting itself whenever I turn it on. First the CD drive will make noise and then the power startup sound cones on. I get a white screen and then the apple logo appears on the screen. Right after that a loading bar will appear on the screen. About halfway from the bar bring filled, the screen has a horizontal, gray, fizzled bar going across the top half of the screen. The screen then dims then goes black for 2 seconds. After that a white screen comes up for about a minute or so and the screen goes black again and the process repeats. I called apple support and we couldn't get it to run a health check or anything. The closest apple store is 3 and a half hours away so I'm trying to troubleshoot it myself and I'm stuck. Any help is greatly appreciated.