2000 olds silhouette van transmission


I have a 2000 silhouette with 115,000 miles. I was driving down the road the other day, about 20 miles per hour when my transmission went into coast mode. I stopped and put it into park. It locked in park. Then I shifted back into drive and nothing, in fact, no gears including reverse. The linkage is ok, the shift lever on the neutral switch is moving. The fluid is ok. One interesting thing is that the interior lights go off-under normal circumstances-when I shift out of park into gear. but not now. Any ideas? Thanks