Mac Pro (Late 2013) Dual monitors freeze on startup?

Agreed! Latest update 10.9.5 appears to have fixed the problem on our Mac Pro - 10 restarts without a problem!! Will continue to test but this hidden fix seems to have done the job. Thanks EdAnuff.

Bad news, don't know if it's related, but seems too much of a coincidence. Machine wouldn't wake from sleep and it's completely dead now, doesn't start anymore past the grey screen. 😟

x.graves-

That is expected behavior.

Energy Star power management reduces the power to USB ports while in Deep Sleep, and may turn off certain functions entirely while sleeping.

Should have been more clear, it's not a wake-from-sleep problem. My machine has basically become incredibly unstable about a day after installing 10.9.5. I noticed it when tit wouldn't wake from sleep, but once I restarted it, it either wouldn't get past the gray screen, or if I did get it past the gray screen through the usual tricks, the screen would show occasional screen glitches or random restarts. The only good news is it's no longer a dual monitor problem - single monitor is just as flaky. I'm taking it to the Genius Bar tomorrow.

Genius Bar found nothing wrong and did an OS re-install with 10.9.4. I'm staying on 10.9.4 till Yosemite because it was instability with 10.9.5 that finally made me take it in for service. FWIW, the Genius Bar claimed they tested it with dual monitor settings on Thunderbolt Displays, DVI monitors, and VGA monitors. I really don't think their tests are going to catch these hang-on-start issues. I'm reasonably comfortable that the Genius Bar is correct and that there's nothing wrong with the hardware, but clearly there's as yet unresolved software issues with compatibility with non-Apple displays. Either Yosemite will solve those, I'll switch to Apple displays, or I'm selling this computer and switching to a different model. Overall, I'm very disappointed.

Just an update, I've been running Yosemite RC3 and the startup issue seems resolved as does the other screen glitches I was seeing. Fingers crossed that Yosemite is the solution. It appears the Yosemite stages when it activates the monitors on startup or wake from sleep, with a delay after the first monitor is activated and before the second one lights up. The result is that the machine starts up a little slower than before but doesn't lock up anymore. I wonder if this was part of the solution.

10.9.5 did not fix the issue for me.

Computer: Mac Pro 3.7Ghz

Monitor 1: ASUS pb278q

Monitor 2: Acer h236hl

The Good:

10.9.5 does appear to have solved the trashy-glitch-screen that used to appear on startup.

When I Cmd-Opt-Eject (put displays to sleep), I can wake the displays and have them work fine again.

Acer H236HL works without issues.

The Bad:

The ASUS PB278 is not detected each morning when I come in for work. Often the system acts like it is in dual display setup and uses the other, working Acer monitor as the Secondary display.... even though the Primary (Asus PB278) is just a black screen. Turning it on and off and even unplugging it does not help. I have to restart my computer every morning.