So here I am facing the same exact issue my first card had.  I'm currently on a RMA and it's been working fine, but I came home yesterday from work only to find that my main monitor (ASUS VG248QE) wouldn't come up from sleep.  I immediately felt a sense of dread as I had already gone through this issue and was hoping it was something else, but no matter what I did, I could NOT get the displayport to actually send anything to the monitor.  I run a triple monitor setup with 2 ASUS VP239 monitors to the side hooked up through HDMI (one direct, other through DVI adapter).  As long as I unplugged the DP cable, these 2 monitors would come up and work just fine, if I completely unplugged these and only used the DP, no matter which of the 3 ports I would plug into, nothing would show even though I could hear windows do the ding as if it found a new piece of hardware (the monitor).
 
With just my 2 side monitors plugged in through HDMI, I was able to get back into Windows only to find that Precision XOC was now showing my card with a gpu clock of under 200 and memory of not much more than that.  I went into the NVidia control panel and changed it to max performance and reset XOC and saw it go back to normal levels, only for it to immediately drop back down.  I've been running XOC ever since I got this card and it NEVER underclocked itself like this, same with my original card... it was only when DP started acting wonky that it would do this.
 
Now here's the weird thing... I just plugged back in my main VG248 with one of the HDMI connections from the other monitors and have dual monitors running both through HDMI and STILL can't get a DP signal, but now XOC is showing where the card is running at its default 1700~ 5500~ clocks as it always has (no, I don't run an OC).
 
I've about had it with this particular card version as I know it's had nothing but issues before with others and now I'm seeing this which makes no sense.
 
Oh, and before anybody asks, I have two DP cables and I've tried both that work fine and both are showing the same symptoms, so it's not the cables either.
 
I honestly have no idea what's going on, so any thoughts would be appreciated, because at this point, this will be the absolute LAST EVGA product I use... and at this point, if they want to RMA this one, they might as well just send me a flaming bag (if you know what I mean) rather than another one of these sorry excuses of a card.

So they would work fine for months and then suddenly NOT work... and these other issues would pop up... just because they're not VESA certified?  Yeah, no, they're both certified... and I put in a support ticket but have yet to hear anything.

Bandwidth usage over 13.27 gbps will cause the card to clock up all the time.
 
Two VP239's @ 60 hz a piece will use 7.46 gbps, or 3.73 gbps a piece. The card will run at normal idles speeds (139 mhz core & 405 mhz memory) when only those two monitors are being used.
 
Add in the VG248QE @ 144 Hz and you're up to 16.42 gbps which will cause the card to run clocked up all the time.

You sure the problem is coming from the video card? The input on your monitor may be the cause.

If the prob lies with letting the monitor sleep.. can you prevent the monitor from going into sleep? Or the pc going into sleep mode?