It sounds like it's switching inputs automatically. Are you running both units at the same time, while they're hooked up? If so, try unhooking one and see if the problem persists.
If it still does, you may want to see about an exchange or a repair on the unit. I am sorry to hear that you're having this issue, but keep me posted.
So today I got a new Samsung syncmaster 2494hm that I bought from newegg. So I hooked up the monitor to my computer (dvi) and XBOX 360 (rgb), and all the wires are on there as tight as possible, but I keep having a problem where the monitor starts flickering then goes black, but the monitor is still powered up. So I switch the input back to the input that it is and it works fine again until a few more minutes where it does it again. It happens when both when I am playing my XBOX 360 and on the computer.
Other than that everything works great and it looks amazing just this one problem is really annoying. What do you think the problem could be??