Avast infected

Hello,

Yesterday I had a White Screen.
My Avast license is ok till august 2014 but the program does not protect my pc anymore.
0 days off protection.

I can not delete my Avast, re-install my backup license, nore put my pc in a previous setup.

When trying to re-install my licensed program, this is what the error says:
"Error reading product data from “C:\Program Files\Alwil Software\Avast5\Setup\part-Setup_ais-7d6.vpx”. Setup cannot continue.

What can I do?
Thx.
Quinten

When trying to re-install my licensed program, this is what the error says: "Error reading product data from "C:\Program Files\Alwil Software\Avast5\Setup\part-Setup_ais-7d6.vpx". Setup cannot continue.

follow instructions
Uninstall Utility http://www.avast.com/uninstall-utility
Installation files http://www.avast.com/download-software