Hi, My UPS is this model, brand new. My Mac Pro is 5,1 with two 2.93GHz 6-cores, running the latest snow leopard. Today when I walked into my office, I found that my UPS is making a long beeping sound. The Mac Pro cannot be waken up by mouse and keyboard, and its power light on the front panel is off. This looked like a power failure to me and the computer did not appeared to be running. Then I reseted the UPS and booted up the Mac. So far so good. Just a power failure, not a big deal, right? However, there was not a power failure. I have another UPS whose battery is completely dead. Whenever there was a power issue, that UPS would be off. This time, that UPS ran perfectly. So I am not convinced that there was any power problem. The problem should lie between the Mac Pro and the UPS it is using. What's more weird is that, after I booted up the Mac Pro and looked at the system.log file, it says there was an improper shutdown. The time for the improper shutdown is when I reseted the UPS. It's not some time much earlier (in such a case, I would believe it is a power failure). The exact log is: Nov 14 12:33:31 localhost DirectoryService: Improper shutdown detected So it seems the computer was still running somehow at that time, otherwise it would not know there was a shutdown. There is also a message in the power management logs saying * Domain: sleep - Message: Sleep: Platform Failure - AC - Time: 11/14/10 12:33:34 PM GMT+08:00 - Signature: Platform Failure - UUID: 60CB8E45-A84D-4181-B69B-6B98D84910A3 - Result: Failure This happened twice in the past week. The first time when it happened, there was no data link between the UPS and the Mac. The second time, the UPS was connected to the Mac with USB. The UPS only has the Mac and a WD 4TB external disk connected to it. These two device don't seem to be able to terribly overload the UPS. Plus, when this happened, I am not doing anything on the Mac. On the other hand, when I ran something intensive on the Mac last week, there were no problems at all. So this doesn't look like an overloading problem to me. Anyone knows what might be happening? If the Mac Pro has sleep issues, why did the UPS complain?