Performed SMC. Now gray screen and running gear has been going for a very long time. What to do?

I tried to perform an SMC on my iMac. Now the gray screen and running gear has been "running" for a very long time. I tried to restart the iMac, but the same gray screen and gear came up. When I tried to restart the iMac, a loud tone/buzzer sounded and then the gray screen and gear reappeared. I am writing this on my wife's iMac as mine is inoperative.