iMac would not start; kept restarting once it got to the Apple white screen
My iMac (mid 2011) kept restarting and stayed in that cycle. It would come up to the white screen with the Apple and shut down again. I am hours away from an Apple Store and I work on computers at my job so I thought I'd give it a try.
Turns out that I needed to use my 1GB external Hard Drive I use for Time Machine and restore to a known good date. I did this by pressing and holding the option key until it gave me an option to choose the Hard Drive. It then led me to restoring to a known good date of operation.
I did open the iMac up thinking that it was a power supply issue. Then I ran across a thread that spoke of the LEDs on the main board and what they mean (also excellent way to know if your monitor is plugged in and talking, the 4th LED comes on is all is well).
LED 1 = When ON you have power coming in from the plug. if it is off, unplug for 1min and replug. If it still does not come on then you have no power from the plug or the power supply.
LED 2 = When ON, your main Board has the correct voltage from the power supply (Power Supply is good).
LED 3 = When ON, the main board and video card are communicating properly (Video Card is good)
LED 4 = When ON, the main board and the LCD display panel are communicating properly (LCD display is good) NOTE: I had to reconnect the communications connector several times to get it right when putting it back together. After all the connections were reconnected, I held the LCD display tilted away from the computer while plugging it in and turning it on. Once I saw all four of the LEDs, I closed it up. (In case you have to go back in, be careful to be patient enough to wait after unplugging the power cord... the power supply takes a few minutes to drain its stored power).
I am going to replace my 1TB HD with two 1TB 2.5" HD when they come in. It should be easy.