Q: Imac starts up then shuts down

Don't give up! There may be hope yet.

Did your iMac startup to the light gray screen with a dark gray Apple Logo or does it still remain at a blank gray screen?

Regardless, disconnect all peripherals (directly connected to the iMac) except the keyboard and mouse. Can you get to the User logon or home screen now?

If not, a number of possibilities can be the issue.

The next thing to try is to boot up your iMac in Safe Mode. To do so, power-on or restart your iMac and immediately hold down the Shift key when you hear the boot chime. Continue to hold it down until, hopefully, your iMac boots up to the logon screen.

Safe Mode will bypass all but the most essential system software, so if the problem is with a third-party system extension, then this will suggest that you need to tackle your software and add-ons to fix the problem. If Save Mode does NOT allow your system to boot, then the problem is deeper in the OS configuration and further troubleshooting will be required.

Ok, got it. Thanks for clarifying that for me.

Yes, it may be possible that you are not able to get into Safe Mode because you are using a wireless keyboard. If you do have a wired one handy, it will definitely help.

Since your iMac did make it to the Apple Logo screen, the following could be the reasons why it won't go any farther:

• A required service failed to load
• Stalled network services
• Selections in the Directory Access application
• The Mac is set to search for a particular server at startup and the server is not available
• Corrupt files and permissions errors in the /System/Library
• Corrupt or missing plist files in /System/Library/Preferences
• Missing or corrupt EFI partition.

Please try getting into Safe Mode using a wired keyboard.

I had this issue (would chime, screen goes grey, status bar would go about halfway then it would turn itself off, and continue to do this over and over until i pressed the power off button on the back) and after a month or so of trying to fix it, I took it into the Genius bar and it turned out to be the graphics card was dead. 388GBP to put it right, it now turns on, but I can't connect to wifi. (not sure if this is linked in anyway?!)

I pressed the power button on the back to turn it off otherwise it would be in a continual loop of starting up, grey screen with progress bar, shutting down then starting up....over and over. Only way to stop it was to turn it off from the back. I went through some checks with an online chat apple person that made me hold down different buttons at different times, but nothing would work. The guy in the Apple genius bar said nothing I could do would have made it work as the graphics card was broken