When I install the paid version of Avast it disables my keyboard and mouse in Windows 8.1, What can I do to avoid it?
Remove any version of avast already installed.
Not just through control panel, but also use the uninstall tool.
Install the latest version.
See my signature for link on How-To for clean un-re-install.
It has link for Avastclear but here too: http://www.avast.com/uninstall-utility