To keep it short:
OK, suddenly your monitor is turning off by itself and then on again in strange cycles...
Set the source to TV (not DTV) -> Setup -> Plug & Play.

The first time I run "Plug & Play" I saw artifacts on the bottom of the screen and I got a bit scared so I run it twice and the problem went away.

Now some antifact.

• First my 3 years old SyncMaster 242MP died few months later than the warranty expiration.
  When I bought it I paid it 1200+ Euro.
• I bought 2 SyncMaster T240HD
• Previous SyncMaster had PIP. I could use the PC and watch TV in a small box.
• Previous SyncMaster had radio. I could listen the radio while working on PC
• Current SyncMaster has DTV
• Current SMs comes with 2 identical remotes. When you try to change something on one monitor you'll change something on the other too, unless you stick the remote to one monitor or you turn the other. Annoying
• One of the new monitor has a burned pixel
• One (or both) monitors power on by themself for few seconds at night in TV (or DTV) mode[1]

I'm a bit disappointed considering I've NEC and Philips monitors that lasted more than I can remember without any problem.
Samsung LCD have nice colors and seems to have a good ratio price/resolution, but next time I'll buy a monitor I'll think to invest 50 Euro more in something more reliable and troublefree.

To add pain to my disappointment fixing the standby/power on cycle happened in circumstances that made hard to diagnose the problem.
I just upgraded nvidia drivers and I experienced another problem on the monitor that a bit later started to go in standby for no reason.
I'm using the 2 SM in TwinView mode and the image of one started to be fuzzy. Horizontal lines where moving of few pixel. The first thing I thought was: never buy a Samsung monitor anymore: this one is going to die. "Fortunately" I've 2 monitors and I hope they aren't going to die together.

But anyway I just changed nvidia driver and I thought the problem could be related.
So I fired nvidia-settings and started to touch every settings...
When I changed DFP-0 -> GPU Scaling Method of the "working" monitor, the monitor that had problem started to work properly. Weird. But that wasn't the end of the story.

The day after I woke up, started the PC and the second monitor started to power on/standby by itself.
I started to tweak with nvidia-setting again. Downgraded nvidia driver... till I decided to switch the mon to TV mode... and well it was powering on and off by itself even in TV mode.,br />
I unplugged it (hey maybe the soft went crazy), but the problem was still there. So I thought... maybe there is some setting that got screwed. Let's start the Plug&Play routine over.

[1] shutters were closed and the cat was sleeping with us. I never jumped out of the bed to check what was really happening since it last few seconds.