Personal equipment
Modem: Maxis Home Fibre package, some sort of modem(same as unifi) + Thomson router
Router: TP-LINK WDR3600
Firewall used: Nil

Problem details
Problem description:

Okay my current setup is like so, I have Maxis Home Fibre 10MBPS package paired with Astro IPTV.
Internet comes from the fibre cable to a Modem(i think), then to a thomson router.

Thomson router's wifi range is kind of "not" good enough upstairs. So I had a spare TPLINK Router WDR3600 which I thought of using it as an access point. I googled around, and found some tutorials of setting up routers, even a tplink one http://www.tp-link.com/en/article/?faqid=417

Now I followed these steps and yay internet would go thru and all. After testing it awhile, I went downstairs and Astro wouldn't work, some network error popped up. I pinpointed it to the TPlink router because if I remove the LAN connection between the TPlink and Thomson router and rebooted, astro would come on again. And if I plug the LAN cable back in, after 3-4 mins or so Astro would die off again. Internet would still work on both routers.

Am I doing anything wrong here? I am not a complete noob at networking but I'm not as smart as SIFUs here

Yes I did