alarm goes off when I wake my iMac

I have an iMac with an intel core i3 processor. I inherited it and it was barely used. When I wake it from sleep a loud beeping alarm turns on. I have no functionality with my mouse or keyboard and the screen is black. I have to force quit with the power button on the back. it restarts just fine. It does this on every wake up from sleep mode.

I am running 10.8.5 which I just installed from 10.6. It did it on the older operating system as well. thanks.