Kenneth Branagh's film noir thriller "Dead Again" stabbed a claim to first place at the box office over the four-day Labor Day weekend. The Paramount Pictures release was abetted by good word of mouth and an increase in the number of theaters from its first weekend, which sent grosses zooming 65%. In 47 Los Angeles-area theaters, "Dead Again" did a lively $14,000 per screen; nationally, it scored a strong $8,477 per screen. Overall business at the nation's theaters remained locked in slow gear. The horror film "Child's Play 3" opened to slow numbers. Two of the summer's long-runners showed gains: "Terminator 2," up 2%, and "Robin Hood: Prince of Thieves," up 36%.