Freezing of Mac after the installation of Avast 7.0

I just installed Avast 7.0 on my Mac and less than 2 minutes later my Mac Freezed. This is the third time I am trying to install Avast 7.0 and every time my computer freezed within the hour.

For a third time, I uninstalled Avast but my computer keep freezing.

How can I get out of this vicious circle?

Thanks