My iMac keeps restarting after installing new power supply

The power supply failed and my iMac wouldn't start up any longer. I replaced the power supply and started the iMac up right away. It stayed on for about 10-15 minutes and then restarted. Then again. Restarted a few times and now won't do anything. It will start up fans inside the computer but won't make a startup chime and the screen is blank. I guess maybe I got too excited that the computer was back up and running. Any advice?