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I’ve just bought a 2008 Mac Pro EMC No:2138 running OS X El Capitan version 10.11. It was working fine until it asked me if I wanted do upgrade to the newer version of iTunes. I accepted and then clicked on the “restart now” option to complete upgrade. Upon restart the machine took me to the grey flashing question mark screen. I have tried all start up command combinations, none work except holding the option key which takes me to start up manager. I select desired disc and the screen turns grey, no flashing question mark just a grey screen. I have replaced the PRAM battery as I understand that it can cause boot up problems if it is dead. Still no luck. Any ideas or suggestions would be much appreciated. Thanks
Lets create a bootable OS installer as you’ve got a messed up drive. Follow this guide with a fresh USB thumb drive: How to make a bootable OS X 10.10 Yosemite install drive You’ll need to get some help from a friend that has a Mac that can down load the OS-installer from the Apps Store. While Apple is pushing Mojave for now I would stick with Yosemite for now. If you have anything important on the system now you’ll want to back it up onto an external drive before doing anything. Using the external OS installer drive I would run Disk Utility to wipe the drive and then do a full install. Do keep in mind your system will restart a few times let it do its thing at the end the installer will ask you if you have anything that needs to be restored. This is the point where you can use your backup drive to recover the user accounts as well as the Apps & data.
