Get out of range error from monitor after rebooting from working monitor config I have a Mac Pro 3,1 w an nVidia 8800 GT running El Capitan.  When I reboot, the monitor shows the apple logo with the progress bar. It then goes blank and the monitor reports an out of range error. If I plug another monitor or the same monitor in to the second DVI port without the other monitor being on, the monitor in question displays the login screen without issue. 

I'm confused as to what is going on as when I shutdown the monitor is fine.
Any thoughts as to what is being triggered when I plug in the cable to the second DVI-D port?
I'd try clearing the SMC &amp; NVRAM first…

Power down.
Disconnect all but the monitor with the issue, which I'd plug into the port with the issue.

Reset SMC on a Mac Pro -
Power down. Remove the mains cable from the back for 15 seconds. Press the power button for 15 seconds. Plug back in. Wait another 5 seconds, power on.

Reset NVRAM [do this as it's first powering up from the SMC reset]
At the chimes, hold  Cmd ⌘   Opt ⌥   P   R  until you hear the chimes a second time, then release.

See if you can then get through startup &amp; shutdown twice without seeing the issue.

If all is well, power down &amp; connect the second monitor.

If not, try booting in safe mode &amp; see if there is any change.
At the chimes, hold the  Shift ⇧   key until you see the progress bar.

I've had a couple of Mac Pros over the years, with several different graphics cards. They all seem to get this type of monitor 'memory loss' periodically.