Can you check Events logs on the operating system for any messages related to shutdown?
We have five dell PowerEdge R240 servers. Today, at 3 PM, I was doing some remote maintenance on the server, and I suddenly see on the screen that the machine started to shut down by itself.  Called some guy at the office, and he power it up back on.    Two hours later, the same thing happened. He double checked all the BIOS settings, and all windows logs. Nothing. About 7 PM, the same thing happened again.  The server shut downs by itself.  We have four more servers like that one, purchased on the same date. Any help or advice would be appreciated. 
DELL PowerEdge R240 do a windows server shut down, but I didn't scheduled that.