restart every 5 seconds

From a couple of days my iMac is not booting up. First day it was stuck in the restart loop, I tried to open disk utility using command+r and command +shift +p+r but it wouldn't open the disk utility. Yesterday, it was still stuck in the restart loop and sometimes won't even show the white...

Hi, hope someone here can help me solve this: I have a 2012 MacBook Pro 16gb RAM, running the latest Mojave OS X. I had a 500gb SSD drive seemingly go bad. Replaced it with a new 500 gb SSD. Running fine until a few days in when screen goes blank and MacBook restarts then 5 seconds later...