MBP absolutely refuses to detect external HDMI display!

I am a proud owner of a 2010 unibody MPB, and a recent convert from Windows despite years of dedication to Microsoft. Everything about the Mac is amazing, but after literally days of troubleshooting and trawling forums I have reached the the end of my tether with this issue. No problem with windows has ever taken me this long to find a solution to. This forum is my last resort!

After a brief period where it worked perfectly, my MBP now just refuses to output anything via HDMI to either of my two LG HDTVs!! This is extremely irritating, and I am sure that the issue does not lie with the HDMI cable or the TV's themselves as I have verified this by connecting other computers via the same cable with no problem. I am using a "Cableson" HDMI mini-displayport adapter which was bought on amazon, and from the reviews, it seems to be a legit piece of kit.

The problem I am experiencing is rather strange. I used to have an old 2007 TV by Hanspree, and everything worked flawlessly when connecting it to my MBP. The TV would go blank when the laptop went to sleep, and spring back into life again when I woke the computer. And it didn't matter in what order the cables were plugged in - I have read that this is sometimes an issue. Everything just worked!

I got rid of the Hanspree however last week, and replaced it with two more expensive LG models. Everything worked ok initially, but after the computer fell asleep for the first time (I think this was when the problems began but not sure) everything seems to have gotten messed up.

When I connect the computer to the TV, the laptop screen flashes blue twice, but nothing happens on the TV. So the computer is detecting a display in some way, but not doing anything about it. Clicking "detect displays" does nothing. On the TV, it does recognize that there is an active HDMI input, as all the inactive inputs (i.e. HDMI-2, Antenna, RGB etc) are faded out but HDMI-1 is in bold. If I select the inactive HDMI port on the input list, the laptop screen repeatedly flashes blue until I switch back to the one it is actually connected to, but still I get the "No Signal" message. It is exactly the same on the other LG I have.

But it's weird, SOMETIMES it does work, just randomly. Apart from the rare occasion out of hundreds of attempts that it actually does work, as soon as I disconnect and reconnect, or put the computer to sleep, it's gone again. And replicating what I just did has no effect. I don't have the Hanspree TV anymore to see if it still works with that, but since the computer has connected at least twice since the problems started, I think the problem must be with the OS and not with the cables or TV.

Ugggh! Just look at what I have tried, with no (or only temporary) success:

* power cycling the TVs
* power cycling the laptop
* every possible combination of cable-connection order (i.e. hdmi to dv adapter to mac to tv etc)
* trying to "detect displays" - does absolutely nothing
* powering on the TV while connected to the computer
* powering on the computer while connected to the tv
* connecting cables while the computer is in sleep mode and then waking it
* waking the computer with a usb mouse while connect to the tv in clamshell mode
* restarting the computer with the cables connected
* resetting the parameter RAM and system management controller
* factory reset of the tvs
* tried every available HDMI input port on the TVs

And probably a lot of other irrelevant stuff that I can't recall right now.

One thing that did seem to have worked was uninstalling "Air Display", an application for using my iPad as an extended display. After I did that, it worked on BOTH of the LG televisions straight away with no problems, but alas only until I tried to connect it a second time, and found I was back to square one! I have subsequently tried installing and uninstalling Air Display again but to no avail.

I have searched extensively online, and found that many other people have this problem in various forms. All of this evidence would lead me to conclude that this problem is a software one. Either that or I am completely missing something.

All I really want is for someone to tell me that this is a KNOWN problem that apple are working on to fix in the next update. Because, I need this setup for my work and I think it's going to be an Apple dealbreaker unless I can get it resolved.

I really dont want to be forced to go crawling back to Microsoft with my tail between my legs!

Please help ...