My iMac starts up and then shuts itself down during the boot up process. it shuys down half way through the Apple logo appearing. any ideas how to fix?

Hi daveormond,

I'm sorry to hear you are having these issues with your iMac. If you continue to have issues with your Mac shutting down part way through the boot up process, you may find the troubleshooting steps outlined in the following articles helpful (given your description, it sounds like it could be either issue, or a combination of both):

Mac OS X: Gray screen appears during startup - Apple Support

OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem." - Apple Support

Regards,

- Brenden