Dear abhi_12345,
What registry key did you remove? As advised above use the AVG uninstall tool and you can download a fresh copy of AVG 8.5, which i beleive is free. AVG, in general is going thru' rough times and this forum is regularly seeing "Help reg.AVG"! Since advise is easy to give, why dont you try Avira Antivir(New version)? Finally, it's your choice.Best wishes!
http://www.free-av.com/ .(website of Avira)