Thunderbolt Display - Image stopped working over night, while in sleep mode

Question

Hi All,
Wondering if anyone has this problem?
Been using TB display fine for over a year.  Connected into it are a couple of external usb hardrives, TB WD backup (which has a mini-HDMI monitor connected into it). The monitor has always worked well with the clamshell closed - seems like previous updates have fixed the odd phantom decision of which monitor should come on and when.
Over the night, after putting the monitor into sleep mode, when I woke it up all systems kicked on (I could hear the external drives working and the other external monitor turned on), but no image came up on the TD display. My macbook thought it was on, as I could sweep my mouse over into it and initiate programs on that screen (but just not see them). 
I unplugged everything from the display - still same problem, no image.  When I open my macbook up, while connected, it again thinks the display is active but there is no image.  When I sweep out, my macbook thinks the in-computer display is "Display 4".
Because of the previous nuances with the TD display, I'm hoping hope that this is a software issue, but it kind of seems like hardware.
Any insights would be great!
Thanks

Answer 1

Another update for you all....
While watching a movie on the TV yesterday the Mac Pro and Thunderbolt display went to sleep and once again when I tried to wake them the screen was totally black. I called Apple again and the only thing they could suggest was to take the screen to an authorised service provider so that they can run tests.
After going through the resetting of just about everything I got the screen working again.
I then trawled through forums on various sites and can see that this is quite a common issue - especially if your connected computer is running Mavericks.
Other solutions which people have used are plugging the power plug for the Thunderbolt display into a totally different power source (if that's possible in your set up). Thankfully for me it is.
Another suggesttion which has worked for others is to disable the Power Nap feature within the Energy Saver perference pane.
I did both of those and for the first time this morning the Thunderbolt Display woke up when I woke the Mac Pro!
However I did get an error message that he system had recovered...
Date/Time:       2014-06-15 01:57:42 +0100
OS Version:      10.9.3 (Build 13D65)
Architecture:    x86_64
Report Version:  18
Event:           Sleep Wake Failure
Steps:           0
Hardware model:  MacPro6,1
Active cpus:     8
================================================================
Code: 0x4000c27006700      
Now I know for sure nobody tried to wake the computer at just before 2 in the morning!
The log points to wake for Network Access being the culprit here
Jun 14 23:52:02 Johns-Mac-Pro kernel[0]: Wake reason: RTC (Alarm)
Jun 15 01:51:55 Johns-Mac-Pro kernel[0]: RTC: Maintenance 2014/6/15 00:51:55, sleep 2014/6/14 22:52:02
Doing more digging in the internet I found this article
http://sysadminblogger.wordpress.com/2013/12/02/os-x-mavericks-wake-for-network- access-with-no-random-wake-ups/
So I am now thinking that not only has power nap been causing issues with the display but wake for network access is also not really working as Apple intend it to.
As I am a home user there really is no need for me to need wake for network access enabled anyway so I am also going to disable that. Hopefully this will mean that I have no more random phantom wake ups which I think may have been the cause of this issue all along.