Hi - I bought a 27in 2009 iMac from an auction site cheaply to repair. The owner said it beeped every few seconds, which made me believe it could be as simple as the RAM not being seated correctly. No such luck. I did replace the RAM and the beep went away but the screen remained black, with no boot chime. I lifted the LCD away and it briefly lit up (which has subsequence done a couple of times but only fleeting). Oddly when pulling the LCD away, the PSU, or inverter board start buzzing at varied speeds based on the distance the LCD is away. I convinced myself it was the inverter flex ribbon cable, which had seen better days, so I replaced but with no joy. I have tried different RAM and fortunately have a working model, so switched out the PSU, inverter board and LCD, again to no joy. The only remaining choice is the logic board, video card, or a loose connection. I can’t get an image on an external display either. I just wondered if any iMac geniuses might have any insight. I’m still not convinced it isn’t the PSU and inverter board.