Hi, I have been having real issues with my iMac, I was running 10.10.1 and the Mac was restarting unexpectedly, it didn't matter if a programe was running or not. Started in both safe mode and guest user and still restarted. I tried all the different resets SMC etc, still restarting. Then for a few hours no restarts, I manged to download and update to 10.10.3, although fans were running full speed seemed to be ok, but now it started restarting again. Now about 3 days later it won't turn on at all, no reaction from pressing and holding the power button. I have tried different power sockets and leads. Other issues I was having during this process were black screen at start up and flickering screen with resolution not quite right, showing really cropped images of the home screen to now nothing. I have removed 3rd RAM upgrade and vacuumed (low power) the vents. I have no recent back ups due to my maintaince lacking. Any advice would be greatly received, I would like to try to resolve without a fresh restart or taking to a shop.