A 70-year-old man died in a two-alarm house fire Friday night, officials said. Winchendon firefighters arrived at a 2½-story wood-frame house at 95 Beachview Drive at about 7 p.m. to find the home engulfed in flames, Winchendon Fire Chief Thomas Smith said in a statement. Firefighters tried to locate a person inside the home, but were forced out by intense heat and live power lines downed near the front door. After the fire was extinguished, firefighters found resident Donald Willett dead inside the home, according to Tim Connolly, a spokesman for Worcester District Attorney Joseph D. Early Jr. The cause of the fire is under investigation, the statement said, but it is believed to be accidental.