My IMac 24" intel will not start in safe mode.

Question

Did a Shift - Command-V and the black screen showing all the startup steps appeared and it all looked good except: AFL Alart Sockwed cant update and INIT Reboot transmit failed. All else looks good. I have tried this 3 times and never go past that point. Then the screen turns off white like it does when it starts normally before the apple appears and the last time the screen went black.
I have tried starting with just the Shift Key and computer starts up but not in safe mode.
I have tired starting with the OS X disk and the C key and it will not recognize the disk.I used the #1 disk since the instructions are printed on the disk. Did not work so I tried disk 2 and I get a menu to start the OS or tools. If I click on either one the screen goes white and stays that way.
computer starts fine and provides a login window, and then the desktop screen with screen saver pictures in perfect color. As it goes through starting programs it starts the same programs that is had open when the computer originally crashed. Even when I close them, before it locks up again, and I am forced to restart the same programs open up to the same place. Its like the computer is frozen in one location and will not go beyond that point. Eventually the screen turns white and sometimes black and sometimes gray.
Tech support thought it was the video card, put a new one in but did not fix the problem and then said it was not that but that it was the monitor. I said that did not make sense since the monitor and desktop icons and pictures are beautiful and clear. They then said it was the inverter board on the monitor and Apple only replace the whole thing. I purchased an inverter board and replace it. No change. The tech person said that the computer works find without the monitor connected - I will see if that is correct next. Isn't that a more systimatic testing procedure then trying parts to see if it works? Oh I did do the complete long hardware test. Took about an hour and it passed! Isn't this strange?
I have to replace a monitor that has perfect color and image if it is something simple to fix or replace. Has anyone ever encounter anything like this? Could it be a virus? 

Answer 1

As you probably read everthing was working fine for over an hour so I shut down and put everything back together completely, all monitor screws, aluminum cover and screws and screen cover, unplugged the external monoitor, plugged in external HD's and turned on the computer and guess what the old problem returned. So I unplugged the external HD's and plugged in the external monitor and took the screen cover off and restarted the computer and guess what it is working fine. Doing a disk utility verify first then if no problem I will unplug the external monitor if all is good then I will plug in the external HD's if all is good I will install what I believe is the problem the monitor cover screen.
Your post about the Temp sensor and another post about the cable to the monitor with the temp sensor has me believing that the monitor is getting too hot for the fans to cool down or the sensor is faulty. Which one is the temp sensor? It is the monitor cable that has the little box at the end that screws to the logic board?
How do you know if the secsor is bad or the monitor is overheating and the sencor is working correctly? Is there a test?