Avast won't run; won't install

Hi
I’m having real problems here. I found this morning that none of my MS Office 2010 programs will run. To be safe, I thought I’d run Avast to make sure everything is in order. It won’t run - nothing happens. If I click on the icon, it’s like nothing is there. It shows in ‘Programs and Features’ under Control Panel, but if I click on ‘change’ (to try and repair it), I get: “An error occurred while trying to uninstall Avast Free Antivirus. It may have already been uninstalled. Would you like to remove Avast from the Programs and Features list?” If I press ‘yes’, nothing happens - it still seems to sit there in the list. I’ve tried re-downloading Avast and the installer goes through the process - the bar fills, showing that Avast is installing, but once it gets to ‘full’ that window disappears and I’m back to square one.
I’m slightly worried as I also tried to run Malwarebytes AntiMalware (I just run it for the occasional scan) - it offered an update and once I updated it, I cannot run that (I get code: 1163.)
Help!

Oh, and when I try to load some other stuff (like re-installing Malwarebytes anti-malware), I get ‘error code 1168’ - same when I try and (re-)install Revo uninstaller which also seems to have failed.

Start a topic in V&W and post your logs there: https://forum.avast.com/index.php?action=post;board=4
Instructions (basic diagnostic logs): https://forum.avast.com/index.php?topic=194892.0