I start my iMac and when it gets to the middle of the loading bar it just restarts and does this endlessly. It doesn't have any OS installed, I believe. When I start with the key C press it shows the macintosh hd and the recovery disk. I try to start with the recovery disk and it gets stuck. I even tried starting with a bootable ubuntu usb drive and it also gets stuck. I run diagnostic (power on and key D) and no problem was identified.
When I gave up and put the iMac away I noticed the center lower region of the iMac was extremely hot. What should I suspect might be the problem?