Q: iMac restarts over and over. Help! OSX 10.11.3

Just one week ago, I updated my iMac 21" to OSX 10.11.3 via App Store. For the first days it was working fine, but now it suddenly crashes and restarts by itself, sometimes showing the kernel panic screen, some others restarts and after a few minutes, even about a hour, restarts again.

I have even reinstalled the 10.11.3 Combo Update and even Delta Update downloading them from Apple Support page, thinking it will arrange the problem, but no, the computer keeps restarting over and over.

After the update, I haven't installed any new software, but I don't know if it is a conflict of the Update with my machine or it has conflicts with any installed software.

Already ran Disk Utility to see if it could fix any problem, but it does not indicate any issue and shows everything is fine, but that's not the true.

Can someone help me?

I can't work like this expecting that in any minute will restart. Obviously, I save my work progress every time.

Julian.

iMac 21" late 2014, 10.11.3.

Thanks!!