My solution for Monitor goes black/standby randomly

My specs (relevant here): OS=Win7-SP1-64bit,
Mobo=Asus P8P67, CPU=i5-2400, RAM=8Gb (2x4),PSU=Corsair CX500,
SSD=Samsung 830-128, Graph.card=Sapphire HD7770-1Gb, Monitor=Dell 2209WA

I think it's always interesting to know the whole history of such things. Mainly because knowing it, you can make your own conclusions, which helps you to find solution for your case.

It all started when I plugged in my new headset microphone (also see http://www.sevenforums.com/sound-audio/377331-my-solution-microphone-not-loud-enough.html ). Drivers installed, removed, installed another driver... finally it worked.
At the same day it happened my monitor went into standby mode all of sudden (screen became black) while PC was still running normally (I could hear music playing in WinAmp). I moved mouse, pressed buttons on keyboard, switched monitor on/off... nothing -the only solution was PC reset or turn off.
And don't even ask: yes, I checked my power savings
Btw. black screen happened quite random: sometimes after 30min's, sometimes after 2hrs -so it was difficult to checks things out.

Darn drivers (my thoughts at that time).. Ok, Win7 was installed almost two years ago and a lot of stuff was installed/removed during that time.. maybe it's time I make I clean Win7 install... and done.
Initially I only installed software that worked fine in past year. In short: that didn't solve my problem.

It's interesting how we make conclusions.. bough new headset, installed drivers, troubles appear.. it can only be headset or driver. It's like thinking: my PC died while I got me an icecream, so fridge must be the cause.

As I've noticed monitor went black only when I ran some 3D software, so I concentrated on graphic card (especially after reading many forums). GPU-Z installed... ran some 3D graph.intensive benchmark for over 30min's.. everything ok. Now I ran HWmonitor -software that displays state of all relevant hardware (I started to assume it's CPU). In short: temperatures were within the expected range -still, monitor went black now and then.
Time to start gambling: it "must be" graphic card.. so I bough new Sapphire R9-270X. Installed and started my 3D app.. much better performance, btw.
And after awhile, black screen again! This isn't happening.. this can't be true

What after to look now? Monitor? .. monitor doesn't care if it's 2D or 3D app running.
PSU lack power? ..but it had enough power before -at least for previous graphic card.

Let's see HWmonitor data again... voltages... wait! +12V rail only shows 11.5xx Volt? Not sure what tolerances are allowed, but being lower doesn't seems to be good...
Shall I gamble again? Of course! Bough and installed new Corsair CX600 PSU
Now I checked voltages again and.. 12.1xxV all the time! -and no more black screen (fingers crossed).

I hope above article will be of some help to you.

Sounds more like your inverter is just going and the screen is shot and it all happened at the same time so you think it was the gpu, what model monitor is it and does it have more than one kind of input? Also what input are you using with it in general and when its black is the power light still on or does it go to standby? That psu might be a little low for load with a 270x but not at the desktop or in a browser so its prob not that.