This morning I returned home to hear my APC UPS emitting a constant tone and the Power On light was unlit. From the guide that comes with the unit, this means that there was an overload shutdown while on the battery. This implies two things: 1) There was a power failure somewhere in the building, which there wasn't because no clocks reset; and 2) That lot's of power was being used while it was on battery, but my machine was in sleep mode. This UPS is only 3 days old, and this is my first experience with a UPS. I'm wondering if there is some kind problem with the unit. Also, it seems the Mac Pro has some kind of built-in fail safe in case of a power failure. When I switched the machine back on, my desktop came up right away, but it was in a low intensity gray-scale, and there was a progress bar showing it coming back up to a normal state. At that time, the color and normal intensity was reinstated.