I have a Macbook, which i am using to communicate this problem. This uses the same mail address as the i-mac and is open for communication now.
I have replied and await your diagnosis of my problem
I do not have an additional monitor
I have powered up the i-mac and cannot see any pictures using the flashlight.
I have turned they-mac on with the keys you suggested held down . The front light came on and the gong sounded but no further response. The screen is bland and the front light has now extinguished.