Just one more thought and I'll quit bothering you. Could it be a wake up setting in BIOS? I know with Dell you have limited settings, but just a thought. Or could it be a server side setting?
Also in the FWIW department, my Sister teaches computers in a small private school. All of the computers started shutting down at the same time every day. After a lot of hair pulling and investigation, it was found that one of the students had decided to play a joke on one of his friends in the next period. He ran a batch code to shut down the computer at a certain time. All of his friends thought that was cool, so they did the same thing. It took a lot of what you are doing to figure out what was going on. BTW, that student who started it happened to be her Grandson.