Problem with Mac Mini

[Richie Gardenhire]

Hello, I have a two-year-old Mac Mini that, when I start the machine,  
it keeps restarting.  I have checked all connections; they are fine.   
I checked all outlets; they seem to be working. I even did a firmware  
update by holding down the on/off switch, till I hear the beep.  Short  
of reinstalling the software, is there anything else I have missed?   
It was working two days ago, so I don't know what happened; I'm very  
careful around the work area.

Richie Gardenhire, Anchorage, Alaska.