system
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Oh yeah I had been having the same problem with having the latest version of Avast and ZoneAlarm running.
Thanks! Yes, indeed it was the problem with ZoneAlarm. At first I had stop all the running shields on Avast and my browsing seems to be working again. Later I started all the Avast protection shields back and once again internet access was blocked. After your suggestion, I shutdown my ZoneAlarm, the problem vanished again. I suggested what you said about deleting all the avast rules on ZoneAlarm program control list and again allowed access to internet by Avast. It’s resolved now. Thanks for the suggestion 
PS. Sorry about my poor English.