Why does it start and stall?

It starts, runs and drives for about 30 minutes then it just dies. The radio, windows and air all work the key acts like it wants to turn over but it won't. If I return a few hours later it starts again and repeats. I know that the antifreeze hose has a leak and the power steering container and hose need replaced. I just want to know was is causing the start/stop cycle before I attempt to take it to a repair shop.