I'm not sure what you mean by motherboard address ...
I will take a bet and guess that you want the MAC address for the network card that is being used to access the said php page. Sadly I don't know of a way to find a mac address from the internet, since a computer is behind modem, router, etc and first thing you would return is the MAC address for those devices before you get to computer's network card.
Hi AnbuSelvi, sorry for my bad english,
I am also asking the same question,
I did not understand if you want the serial of the server machine,
or those who connect to the site?
the latter case it seems almost impossible
to get the serial of the server computer, is what I would me too,
you should write a dll in c++ and put it in php dir estension