internet not getting connected to desktop and getting connected to laptop and other devices via WIFI

Hi,I am using Airtel broadband.1. I am unable to connect to internet from my desktop via Ethernet and when connected to laptop via Ethernet able to connect to internet and WiFi also working properly. i formatted the desktop OS twice and even now after restarting the system internet getting connected and after 5 mins its not able to connect getting error msg as Page not found and when ping from CMD prompt its displaying as Request time out.2. when connected to desktop through Ethernet the WiFi is also not getting connected to other devices.Please give me a solution for this ISSUE.