Chosen Solution
I have replaced the HD in my iMac with the exact same new drive and also replaced the vertical hold ribbon too. When I first stared the system it appeared to start up but the screen was black so I switched it off and checked all the work I had done. I found I had split one of the connections on the new VH ribbon so I trimmed it back and bared new copper so that connections could be made. I switch it back on and nothing! No power, no fans, no screen no bong - Zip nothing! Does anyone have any ideas?
Look to see if you are getting any LED diagnostic lights. On some machine they about the middle of the logic board, on other to the lower right of the RAM slots. Let us know your findings. UPDATE Replace the power supply. iMac Intel 27" EMC 2309 and 2374 Power Supply Replacement
