hey and welcome to the avast forum. we need abit more information from you if we should be able to help you.
to start what os are you using
what version of avast are you using program version free,pro,suite,premium?
are you using the latest version of avast?
any other security program like a third party firewall?
if you like a check up please follow this guide and attach the log of Mbam,OTL and aswmbr (does not work on windows 8 and 8,1)
https://forum.avast.com/index.php?topic=53253.0
good luck