The Chilling (1989)

Universal Cryogenics is doing a booming business in freezing the bodies of the recently dead in the hopes of defrosting them later when science has discovered a way to cure what ails them. Things are going well until the storage facility loses its power during a storm, threatening their frozen clients. To make matters worse, a lightning strike causes the bodies to revive as homicidal zombies. What has the cryogenic lab been doing to its customers to cause this kind of change, and can they stop the zombies before their rampage goes out of control?