Need a Router to work with DSL-2750U

I was currently using bsnl wireless modem 1020-AN as a router in other room. Since last week it started acting weird. When i start it, my internet pings go very high around 5000 msec +. When i keep that bsnl modem shut, net works properly. It was working flawlessly until last week. No settings changed. Now i need a 4 port wireless router which will work with my primary modem 2750u. Any suggestions to this and my problem? Thanks

PS : Admin Please move it to appropriate section if this is wrong.

2750u already has an inbuilt router, it's a modem + router

I want to extend my range and need more LAN ports, hence i want on more router which will be connected to my 2750u and should work as a switch using DHCP relay.