1. SP3 is required for avast. Sp2 has too many risks of trojans viruses will get in to your computer (port risks).
    2.Did you have any other antivirus on the computer previous to avast? if so what was it? Nortons macafees have their removal tools.
  2. Download and update Malwarebytes antispyware. Run malwarebyes free antispyware to see what it finds and remove.
    reboot computer.
    re instal or repair avast through add and remove programs.