Hurt by $43.8 million in start-up and operating costs connected with its Ha! cable comedy channel, Viacom Inc. reported net losses for 1990 and the fourth quarter. The New York-based company’s net losses for the year ended Dec. 31 were reported at $89.8 million (840 a share), versus net income of $131.1 million ($1.06) a year ago. Revenue rose 11% to $1.6 billion from $1.43 billion. Viacom’s losses for the fourth quarter widened to $87.4 million (820 per share) from $29.1 million (270).