IMO, while airing Dallas in Romania was a factor, it was not the only one (though it probably inspired the Romanian people to think, "Why can't we have nice things like the people in the TV show Dallas (1)?"). By the time of his overthrow, Nicolae Ceaușescu had become really hated in Romania (when he and his wife were killed, hundreds volunteered for the firing squad) for a wide variety of reasons. Among other things, he had banned birth control in Romania to cause population growth (something that the What Madness is This? *Republican Union would envy), resulting in lots and lots of unwanted children (it was five children per family; many of the "extra" kids were thrown into orphanages that were described as "gulags for children" and helped play a role in his downfall in 1989), started a personality cult that would have Stalin going "WTF?", destroyed many old buildings in Bucharest (and replaced them with Stalinist-style apartment blocks), exported everything to help pay off Romania's debts (causing rationing, shortages, and starvation for the Romanian people, and creating unrest), and, overall, was one of the worst dictators in the Warsaw Pact (which is really saying something, given how bad the Warsaw Pact was)...
Ceausescu was going to fall eventually; it was only a matter of how bloody it would be...
(1) Never mind the fact that Dallas was about a wealthy oil family, but that's another topic for another time. Also, there was the fact that even the poorest characters in the show would be well-off by Romanian standards...