Is your modem doing NAT? (sharing the internet connection?)
(Is it a router modem? ) (is it a gateway?) ... (all are the same question...

)
will you have computers in your lan?
If yes for all, then your WAN ip is wrong.
Try 192.168.1.100 for example.
put 192.168.1.1 as your gateway and 255.255.255.0 for your WAN mask.
Don't forget your DNS (which should be your router modem)
If it is a simple modem, then DDWRT will have to do both hotspot and router. This is possible, but has to be tested before. I think you will have to use ddwrt v24 for that.
what did the ping say?
ifconfig?
then try to ping your gateway