What's going to happen in 2038???

Can some one explain(in a language that I can understand) what's going to happen with the computers in the year 2038? Something about the clocks (time) on the computers that run Nuclear Plants and other important things like that. I heard that there will be a Nuclear melt down? I don't know....Please help.Thanks!! will melt down because the clocks shut down. Or something like that huh.../ What is Unix time??