I have 3 Mac Minis (2008 models) controlling three lobby display monitors. They each run continuously day and night. The monitors cycle on and off at preset times. They've been running fine for three years. I just upgraded them to Snow Leopard. Now at some point every night, all of the Minis turn themselves off, a complete shutdown. The energy saver setting is turned off. I can't figure out what's going on. Any ideas?