Setting up fibre home adsl modem with linksys wifi router

Salam All, I would be very much thankful if anyone could help me through this.

I just got ptcl connection with a fibre home adsl modem. Now the problem is i want to connect linksys wifi router to it but dont know how to setup both because when i connect my desktop pc through a cable from lan port 1 of linksys router and through other cable from lan port 2 of linksys router lan port 1 of adsl modem. Now when i start surfing net on my desktop pc and at the same time on laptop through wifi it only works for hardly 2 3 minutes then it gets limited connectivity on both pcs.

But when i directy conect only my pc to lan port 1 of adsl modem it works perfect .

What i think is some ip conflict problem. Plz help me through this.

Disable DHCP service on WiFi Router.

then which option should i select there are some other options in drop down static ip,pppoe and etc