Hm…maybe a clean install will do!
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Download the avast uninstall utility here:
http://www.avast.com/uninstall-utility
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Download the avast internet security here:
http://www.avast.com/download-thank-you.php?product=ISE&locale=en-ww
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Uninstall the avast present in your system using the ‘avast uninstall utility’ (The one in step 2) via Safe Mode
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Reboot your computer
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Finally run the avast Internet Security installer ;D
I hope it works 