A. First, be sure to get rid of all remnants of your prior installed AVs.
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=574
http://singularlabs.com/uninstallers/security-software/

B. Drop Spybot…!!

C. 1. Download avast! Free Antivirus: http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe
2. Follow instructions: http://www.avast.com/uninstall-utility (Run this tool for all prior installed avast! versions…!!)
3. Reinstall avast! with the downloaded installer from point 1.
4. Reboot.