Can't install Avast Free anymore

This is the first time that I have problems in my PC trying to install Avast and let me tell you how this happened.

1.-I uninstalled comodo firewall and Avast free the propper way to install AIS to try it for 30 days
2.-When I was ready to instal AIS everything went fine after Avast said that is was finishing installation a BSOD came and restarted my computer
3.-I uninstalled AIS the propper way and went back to install Avast free
4.-Now every time the installer is ending to install Avast free the BSOD comes and re-starts my computer
5.-I have done this 4 times already without success.
When the pc comes back I see Avast is not working my pc says I don’t have the antivirus but in program files Avast is there with all its files.

What to do? where to go? I don’t want to be without my avast.

Did you use the uninstall utility…?
http://www.avast.com/uninstall-utility

Yes I always use the Avast uninstall utility.

I solved this problem using system re-store, after that I had to uninstall Avast and re-install and now it is working again…rm