DHCP failure after installing new modem

So I needed a new modem. I made sure it was on Comcasts list of approved modems. bought it brought it home and set up to install it today. Everything was great up to that point. So as soon as Grace ( the comcast tech) got everything done on her end and booted the router back up the router no longer gets a signal.  The modem works perfect and so did my router until the swap. Now whenever I use wi-fi I get a DHCP failure please contact your ISP.  I have read in here where other have had similar issues ..I am not sure it is the same.  I spent the last 2-3 hours on tech chat trying to work it out.  I was told to update my drivers .... I looked there are no updates for any of my equipment including the modem and router. Help!