Can't connect Wifi devices to router when wired Ethernet computer is connected

I have a arch desktop with samba and ssh configured connected to a WiFi router/ADSL2 modem via ethernet.

I was not able to connect any of my mobile devices (phones and tablet) or my netbook (running windows 7 basic) to the WiFi router suddenly a few weeks back. The issue resolved when I removed the PC Ethernet cable from the router (when I disconnected the PC from router).

My router is D-Link DSL 2730 U

1. 
   

   On logging into another user (not main user) everything works fine.

   
   


2. 
   

   Nothing changes when I stopped samba and ssh services. Infact these services which are configured as root, start before the login

   
   


3. 
   

   I use console without any gui to login. I startx manually after logging in. This problem does not occur on logging in. It starts only when I startx

   
   


4. 
   

   On using wireshark to capture traffic on the ethernet port, this line keeps repeating:

   
   

   
   0.007238000 192.168.1.100   224.0.0.56  UDP 1334    Source port: 38854  Destination port: 46198
   
   

I have no idea what to do beyond this. The internet works fine when logged into main user. However other devices are not able to connect.

Please tell me how to resolve this and what is happening.