How do I find where my DHCP server is on my network?

I have a home network, a BT server, with an iMac, a MACBook Pro, two back-ups (Airports) and a Squeezebox (for internet radio). The problem is that the Squeezebox keeps dropping out and informing me that it cannot find the DHCP server. This did not used to be a problem, has happened failry recently, for no obvious reason. Any help is much appreciated.