Just checked. There is nothing in the sanbox window.
Edit: Should there be anything in there?
Only if you've got avast! automatically running as sandboxed.
Right-click the the browser icon you use on the desktop (assuming you've a PC or laptop) and select 'Run in sandbox'. Steps are the same for running avast!, not that you need to, as Google Chrome was used as an example. You should now see the same thing as in the attached .png file if you run Chrome or other browser as sandboxed. Best setting is to manually select only 'Run in sandbox' when you need to, which is 95% + of the time here. Use care as to what programs, if any, always run in a sandbox.
Was looking for a setting that set the icon to 'Always run in sandbox' as that would/could prevent permanent changes to settings in avast!; if it were set to 'always run in sandbox' and could be a possible source of your issues. Sandboxing a program isolates it from the real/main operating system and prevents unwanted changes to both the sandboxed program and the real operating system as one is kept isolated from the other.
Clear that avast! is not set to 'Always run in sandbox' from what you said.
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Advantages to running a program sandboxed:
Example: Your browser, Firefox, is attacked by ZeroAccess, and the malicious payload is deployed within it. However, since Firefox is not in the actual real operating system environment, but running in a virtual one created by the sandbox, neither the real Firefox or your os will be affected/changed after the virtual Firefox is closed and the malicious contents of the sandbox is then emptied/cleared. BTW, setting the sandbox to automatically dump all contents when using a browser/closing a browser will help control internet junk accumulation over time as it can be trivially tossed when done.
Was your version of avast! gotten from here?
http://www.avast.com/download-thank-you.php?product=ISE-ONLINE&locale=en-ww Decline the online installer and click the full offline installer found just under step #3 if you think you need it.