Just off-hand after a quick look-over this thread, sounds like the format is not being burnt or selected correctly. A movie dvd needs to be in UDF format. Programs like nero & roxio will do this for you if you choose video format & choose dvd as output. The fact you can play it in your computer but not set-top player suggests it's not in the appropriate UDF format. Also don't burn it too fast! Choose a lower speed.

The other thing is your set-top player. Some don't play dvd-r's & some of the better known ones (I know panasonic to be one such one) will only play their own brand dvd-r's. So I'd check your manual or/& go to their support site to find out which dvd-r's they recommend.