Hello all,
I had a problem with my Avast Internet Security where during an update, my computer restarted by itself. When it started back up, I found that Avast had gone. The file was there, but I couldn’t open it, getting the error code: 0xc0000005. After looking at the forums, I decided to uninstall it and reinstall it to see if that will help. I was able to uninstall my Avast, but I don’t see how to reinstall it without having to purchase it again and I can’t find this information in any of the forums. Any help with this? Thanks.
Hi elpeciss, welcome to the forum 
Download Avast! Uninstall Utility to your Desktop.
Get ( resend ) your Avast! Purchased licence again.
Download Avast! Internet Security
Disconnect from the internet.
( Uninstall Avast! via control panel. )
Run the uninstall tool and accept the reboot to safe mode.
Once complete reboot your system.
Reinstall Avast! with your purchased licence.
Greetz, Red.
( EDIT : I forgot the smiley in my welcome. Big mistake ! )