Imac 27 black screen

[Geoff Turner]

Hi - hope someone can help me diagnose this fault.

Imac 27" late 2009

Was on Mavericks - now new HDD and reinstall of mountain lion

The fault was present before the HD and reinstall of OS

I have disabled sleep and HDD shut down etc.

• So, if the mac goes into sleep mode either automatically or if I click on sleep, it will not wake again with mouse or keyboard, bluetooth or wired.
• If I shut down holding power button and restart it "sounds' like all is working but black screen.
• I have to switch on and off a number of times then hey presto normal grey screen and boots up fine - all works great until I shut down or put into sleep mode then here we go again.

I have reset SMC/PRAM etc

Tried to run with diagnostics mode D or shift D on start up but can't get that to work - also a bit awkward because sometimes the screen starts black ....


I am thinking its not software due to new HDD and reinstall of OS

Graphics card?? Display??



Please help



Geoff