If you have got your computer running without avast. Download asw clear removal tool. Save to desktop and run it.
It will boot you in safe mode.

Un install all versions of avast and reboot each time. Version 6 & 7 & 8 & Version 9 each time.

Any traces on your sony laptop of previous antiviruses that come bundled with your laptop operating system original sony dvd rom install disk.

Some come bundled with Symantec /Nortons 360s & macafees etc that need to be removed before using avast that will conflict