Bipolar disorder affects some 7 million Americans – and entertainment superstars have not been spared. In a special report, RadarOnline.com can reveal the stars who suffer from manic depression’s soaring highs and soul-crushing lows. LINDA HAMILTON With muscles bulging on her sinewy frame, Hamilton scaled the heights with the hit Terminator films. But the 68-year-old fought a desperate inner battle for 20 years before she was finally diagnosed with bipolar disorder in 1994. “I really was crashing and burning,” Hamilton said, adding she “spent many years, you know, not only looking for the answ…