Dial tone not present at fxs

respected all,
i m new on asterisk n tdm.i m doing project on tdm.
i have installed tdm410p by using manual at digium site.but port2 and port3 are not installing. only port1 and port4 are installing.further after changing my dial plan(extensions.conf) and system.conf and chan_dahdi.conf…no dial tone is present at fxs port…infact phone attached at fxs port is completely dead.
plz guide me what configurations i should check.
thnx to all