How are you connected to the router? Is the router working at the moment (can you see the router through the PC?) if not you may want to set the router up via an ethernet cable first and then go wireless.
What ISP are you connecting via and what operating system and broadband modem are you using?
It may not be necessary to clone the MAC into the modem but you could have a read through
here and then ask for further help if that makes no sense to you.