Whats is this switch? (6 Pins with FD written on it)
I assume being a power switch one push turns on and another turns off? If so it's what I'd call a DPDT latching push button, although there may be other names as well as sometimes different terminology is used between regions. A search on e-bay at the moment for example using that term shows this product which looks pretty similar:



As well as checking physical dimensions of course also be careful when looking for a replacement to make sure it has the necessary voltage and current rating.

The usual configuration for that sort of switch will be when actuated / pressed in the middle left pin will be connected to the rear left pin, and the middle right pin will be connected to the rear right pin. When disengaged they middle pins will connect to the front pair of pins instead. When used as a simple power switch if you look at the PCB you'll probably find that the front two pins aren't connected to anything.