All, I tried an SSD Install using a SATA Y power splitter, and on reassembling everything, the display would just not come on. This was on a mid 2011 Imac - 21.5" with 500 GB hard drive, and 4 GB memory. The machine would appear to power on (chime) but nothing would show up on the display. The 4 tiny LEDs (obscured by the sound ribbon cable) appeared to be lighting up. I removed the SSD, and put everything back together, display was still dead. I obtained a Thunderbolt to DVI adapter, and connected it to an external monitor. I was surprised to see that the external monitor worked. Was kind of resigned to use my Imac as a grotesque mac mini (and attempt to replace the LVDS cable and connector on the mainboard) - but surprisingly, I noticed a change in behavior a few days later. The white screen and Apple Logo would appear, but screen would turn black, and the external monitor would light up and display the apple welcome screen. System information would only show the external monitor - it was as if the LCD did not exist. Suddenly, everything has started working again. And it is working perfectly. I did not know how to run the Hardware test (I tried multiple times, before I realized that I have to either have the DVD in, or install the tools) initially, but the test no longer reports any errors. I am posting because I am totally flummoxed about what could have gone wrong - and why it corrected itself. I was very gentle with the LCD removal, and I do not think I damaged any connectors. Hoping some of the experts will have ideas about what could cause these symptoms. Thank you for your time.