Screen goes black while using new imac- music continues. can recover by switching off and on

Ok my screen had been going black for the last two weeks and the imac i love and spend most of my days on, had almost become a $3500 boat anchor.

So after pressing every key or keys at startup to wiping the harddrive three times reinstalled the operating system 5 times and ringing Apple two times to no avail.

I pressed the shift key last week and that gave me enough time to go to the apple sign top left/ click on system preferences then energy saver the light bulb icon.

I slid the range computer sleep to never and the display to never. This fixed it for a week. I thought I'd had fixed it yah.

Anyway today it did it again and again, to the point where you could turn it on and within the two apple startup signs it would turn the screen off.

I rang Apple, and while they had me hold i had a play, I turned the computer off and ran my hand over the whole keyboard five times pressing all the keys down as the hand went over it. It started up normally, OMG i thought surely not i thought, meanwhile the apple tech came back and asked how i did it. Ok he said if you restart it will it still go, and yes it has and ist has been going for the last three hours without a hickup.

I did find over the two weeks if you unplugged the imac and plugged it in in the morning it gave me enough time to run things like CCleaner and adware remover not that they did anything to improve the problem, but the energy saver has.

Best of luck i do hope this works for all of you with this problem.

Cheers Hamish.