Cnnecting cabel modem to a router

HI, well I am trying to connect my Linksys "Etherfast Cabel/ DSL Router"  to a cable modem. But the Linksys router is UNABLE to get an IP address form the  modem. but when I connect the modem to the PC, I am able to get the IP (DHCP) from the modem and no static settings are involved. so here are my questions:-

1) do I need a straight or cross over cable to connect the modem to the router?
2) can a DSL router act as a regular router (I have changed the settings to obtain an IP automatically
 and finally
3) if the cable modem is connected with straight cable to the DSL router, why would the router not get an IP form the modem, when PC is able to get it?

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