Just recently I've run into an odd wake-from-sleep issue I'd love some help with. It's a 2010 Mac Pro 5,1 running 10.8.4. I'll describe the symptom and what I've tried thus far: Symptom: Machine goes to sleep, and monitor goes to standby mode, as expected. Light on front of MP starts to "breathe." All is as it should be. I wake up MP by hitting any key...light on MP goes to steady, as expected. Monitor briefly wakes up, then immediately goes into standby mode. The MP appears to be awake, but the monitor indicates there is no signal from the computer. I can hold the power button down to force the MP to power down, and then I can successfully reboot. This sequence is repeatable as often as I'd like. What I've tried, all without success: Reset PRAM Reset SMC by powering down, unplugging MP for 20 seconds, plugging back in for at least 5 sec, and then rebooting removing all PCIe cards except for by ATI 5770 booting from a drive with a completely fresh install of 10.8.4 connecting the monitor via a display port to HDMI cable instead of the DVI cable I usually use deleting the com.apple.powermanagement.plist file removing and reseating the video card I've plumb run out of ideas as to how to troubleshoot this further. Does anyone have any ideas about what else I might try or any idea about what might be causing this? It just started suddenly about 48 hours ago, without any software installs or any other changes that might account for this. Thanks!