<snip> i restore back from quarantine but when i scan again avast doesn't detect as potential thread 
It would have been safer for you to re-scan the file while keeping it in the Virus Chest where it is safe. You can right click the file in the Chest, then scan. If the file is still infected, you should keep it in the Chest. If it is not infected, then you can try to restore it or delete it.
If this file actually was infected malware, you let it out of a safe area (the Chest) and into your machine...not recommended. So in the future, do it as I stated above.
Perhaps what you put in the Chest was a false positive (FP) and that is why you do not see it showing up as a threat now. Are your Avast definitions up to date? Did you run both a Quick or Full scan, and a boot-time scan? If not, please run them and report back your findings. Put any infections in the Chest again and give a screen shot of the Chest in your next post if you have an infection. You can also upload the file in the Chest to Avast for analysis, and this is done on the next virus update.
It does not say in your Signature what version of Avast you are using (other than Avast 6 Free)? Can you tell me if you are using 6.0.
1125 and update your Signature? If you do not have the current version, I suggest upgrading to the current version as well. Thank you.
