iMac screen goes black

[Abenaki]

I encounter a problem in recent months, and I cannot able to solve it. The problem has emerged since I connected the iMac a TV (Philips 32PFL5403H) with mini-DVI / DVI + DVI-HDMI cable. when I finished using the Mac, I press the power button to pause. when I need it after some hours, I press a key on the keyboard to wake it up, I see the screen half a second, and then the screen goes black (the mac is running, but the screen is off)
Several ways to turn the screen:
- If the DVI cable is connected, I unplugged, the screen goes blue, then the screen appears
- If the DVI cable is unplugged, I plug it in, the screen goes blue, then the screen appears
- I put it back in standby with the power button, I immediately rekindles the screen turns blue, then the screen appears
But it is not systematic, sometimes the screen stays black ... desperately. In this case, I put it to sleep, I unplug the power cord, I reconnects and then turn on. Again, this is not systematic, try with or without the cord DVI-HDMI, short, it's pretty galley!

[Devasis]

I've just realized that I have exactly the same problem with my iMac. While it is usually in standby mode, this time, not turn it back on the screen remains black. The only way currently to "see" is through screen sharing from my MacBook. Well, this solution is not feasible in the long term, so besides the VAS, I'm looking for an idea I also address this problem.

[MrChris-]

Since my visit to Snow Leopard I have this problem of black screen to restart and when he gets out after a great time while the system is idle. The solution is to reboot. This looks like to be some kind of internal bug which is causing the problem. You have to check the properly or else it wont be working well. You can take the backup and go ahead with full restoration.

[Calvin K]

This makes twice in one week that my iMac screen suddenly becomes black while I work on Lightroom. The first time the screen was completely black, the second it was black with some white vertical lines. When the screen goes black, it is impossible to do anything, nothing appears not even the mouse pointer. I am forced to shut down the iMac and reboot, then everything is fine. Yesterday, I called Mac support, they made me correct access rights for files using the software to repair disk. They made me do a test with the hardware installation CD but it did not detect anything. From my side I suspect the graphics card but how to prove? Does one of you has already encountered this problem? Is this perhaps a problem of access rights to files (I have big doubts)? Is this perhaps a bug in the Lightroom, the sudden I went from v2.4 to v2.7.