Avast Free Anti-Virus (latest) Serious Conflict with Windows 7 OS

I am using Windows 7 OS, I downloaded Avast Free Anti-Virus (latest) and installed it.
But there seems to be a Serious Conflict of Avast with Windows 7 for the past week in that:
After installation of Avast, my OS crashes. Repairs with Windows 7 DVD “restores” the OS to a point previous to the time when Avast was installed. But, thereafter, Avast stops working:
There is a Cross Mark on Avast icon in systems tray, and when clicked it pops up a window that says “Your System is Unprotected … Resolve …”, but when I click “Resolve” nothing happens.
After I uninstall Avast, Windows 7 operates alright. But when I reinstall Avast, Windows 7 again crashes – Repair with Windows 7 DVD fails UNLESS “System Restore” Option is opted.
So, this leads to a fresh round of the same vicious cycle.

  • OS…? (32/64 Bit…? - which SP/Build…?)
  • Other security related software installed…?
  • Which AV(s) did you use before Avast…?