Hi cool.abhi,
If you are sure that you have completely removed all other A/V programs, and Avast! is up to date, and you have run any windows updates available, then it should work fine.
Have you disabled the Web Shield and were able to browse the web?
Have you tried a reboot of the computer?
Have you done a virus scan with avast, and maybe a scan with Malware-Bytes?
What does your browser tell you when you try to browse? Does it say that the page cannot be displayed, or does it never load the page or something else?