i have been using Avast for a few weeks now, ;D but i must have deleted something i need, to run Avast, :-[ cos now it wont open, a error message comes up, but that wont open either. 
can i reinstall Avast, or download a fix for it???
What error message do you get ? Thanks.
I don’t know if this will help but you try to repair your installation:
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).
You must be connected to the internet while repairing.
If this does not help, can you uninstall / boot / install / boot again?