I also have the problem with the blank screen after monitor power cycle.
I'm running Xubuntu 14.04 on a Dell Optiplex 7010 with a Radeon HD 7570 VGA 
card that is attached to an LG ultrawide monitor (2560x1080) via DisplayPort, 
my desktop is XFCE4.

As this problem is very annoying I googled quite a bit and found this and that 
but nothing really helped.
I also stumbled upon the fact that there must be something weird with 
xfsettingsd: at least under some circumstances this daemon was said to be 
responsible for leaving a blank screen while crashing when the monitor gets 
switched on.

So I had a look whether this is also true in my situation but
xfsettingsd was still happily running while the screen refused to come
back on.

Don't know exactly why (maybe the anger at xfsettingsd to fail somewhere
;-)) but I just killed the running instance and was completely stumped
to see the display turning on again ...

Even stranger is: I tried that several times - monitor switch off/on -
and suddenly it wouldn't lead to a blank screen any more =:-O

Only thing that could happen then was a flickering display; but I could
get rid of that by a forced dpms cycle (via xset dpms force off/on with
a "sleep 1" in between).

When killed with a hangup (SIGHUP/1) xfsettingsd will normally be
restarted automatically (by XFCE session handling I guess); if it
doesn't you might recognize this by different window decorations or so,
just start it manually then.

Hopefully my experiences help someone else, and maybe I have the time
sometimes to dig into the problem ...

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https://bugs.launchpad.net/bugs/1313539

Title:
  [DisplayPort] monitor shows black screen and "no input signal" after
  turning the monitor off and on manually

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