iMac keeps rebooting

Was working on my iMac, and suddenly it just begin rebooting over and over, I got it to restart in recovery mode holding down command option R It said it was connecting online and it had an earth picture that rotated and it did a countdown from 10 to 0 then it went to a white screen with just an apple in it. Is it thinking or recovering or is it froze up, what should I do you?