After a long time I have got the solution of (Break point not hitting in visual studio), so I have decided to post here for my own sake and for those whoa are facing the same problem
Go in Menu, select the option Debug --> Attach to Process
and select the IE. (i.e explorer.exe).
Hope it will work for you also.
Is this because of Internet Explorer Version 8.0?
What you have mentioned is for manual debugging
for debugging the dotnet code, you need to check the Common language Runtime
aspnet_wp.exe - you can attach this one for debugging.