Server maintainence

I will be doing hardware maintainence on our server this afternoon or tonight, as time allows. This will require me to shut down the server for about an hour and I may have to restart it more than once.
This server runs the daffodilusa.org and daffseek.org web sites as well as several other daffodil sites and mailing lists.
The server has four chassis fans and according to the hardware monitor and higher temperatures, all four have stopped. I am puzzled how all four fans could stop so will have to figure that out.
The server will be down up to two hours between 4pm and 8pm PST. I believe that would be 11pm to 1am GMT.
Thanks,
Ben