Not familiar with your converter box, but the usual troubleshooting procedure applies to try to isolate and identify the problem. Do you have anything else that can output NTSC, like a DVD standalone player? Just to verify that the problem is not in the TV. Alternatively, can you hook it up to a computer?
Anyway, you have two suggestive symptoms there: 2 secs of video and/or no signal message. The first suggests the Orei is putting out a signal, the second suggests that signal is PAL, since the TV gives up trying to display it.
Is there any setting or switch on your Orei that you have overlooked? Have you double-checked all your cables and connections? It may be that your converter is faulty.