Version 12 of avast should be running on that system without a problem.

As there have been a huge amount of changes in avast since version 4.8, I strongly suggest to perform a clean installation of the latest version.

  • Remove avast through control panel
  • Run avasclear
  • Remove any leftovers (folder/files/registry entries) manually
  • Install all updates for the OS as well as drivers for the hardware you are using
  • Install the latest avast version