Well... that's your problem... You know what DHCP is right?
If the DHCP host/server isn't enabled (only static), then the N9's WiFi adapter won't be assigned an IP.

Why? Because according to your 1st post, it's expecting to be assigned an IP address that way.
“internet connection failed.cannot able to get ip address from DHCP server ”

You could also statically assign the N9's IP on the router, & then manually enter that address into the N9's wifi settings*
Get someone that's more clued-up about local networking to check your router & your N9 config.

*no idea if N9 does static IP addresses, DHCP, or both, possibly it does both.