Hi everyone, I currently have a problem with my 24" iMac 8,1 . When I turn it on I get fan blowing full speed. I then installed fan control and a sensors app and noticed that none of them even suggested I had a cpu temp and gpu heat sink sensor. They weren't there let alone registering. I opened her up checking connections all were good. I then rebooted and used Apple hardware test and got the 4sns TmOP error. I am struggling to find anywhere what this means and how to fix it. It also just randomly switches off even when fans are at high speed.... Help?