Aporte original por: Mark Rivera ,
ok, the issue was the Video Card after I brought it to authorized service center. I may need a replacement of the video card. Either I buy here or Ebay/Amazon. The case was, Apple marked all iMac 2011 as vintage and all internal parts are obsolete and no guarantee that there will be a service that will do the replacement. Either you do it by yourself or ask a friend to help you.