I have had exactly the same problem using Windows 10 x64 version (uptodate) on a DELL Latitude 3550. I am using Comodo firewall.
The problem is caused by the 'Behaviour Component'. With this switched on it seems to prevent any 32bit software from running.
You are right, you can't uninstall, can't run System Restore, or disable Avast.
My workround is as follows.
1. Start Windows in Safe Mode.
2. Set the 'Avast Antivirus' service to Manual.
3. Restart normally.
4. Go to Control Panel/Programs & Features
5. Select 'Avast Antivirus' and choose 'Change' then 'Modify'.
6. Unselect the 'Behaviour Shield' component.
7. Say 'NO' to restart now.
8. Closedown and restart in Safe Mode.
9. Set the 'Avast Antivirus' service to 'Automatic Start'. (Do NOT start it.)
10. Restart normally.
No requirement to uninstall Comodo (unless you want to).
your solution is really good, below is what i did
1. jump straight into safemode (win key + r, then msconfig, then boot, then, select safe boot, then apply,)
2. complete shutdown
3. reboot computer
4. then once logged into safemode access control panel and select avast then click change.
5. when avast opened clicked change then unselect behavior shield. then finalize the change and exit out of the program after the progress bar for the change went away.
6.then re-did step 1 doing (win key + r, then msconfig, then boot, then, unselect safe boot, then apply,)
7. rebooted computer after full shut down. and no issues
*note: i did not touch commodo firewall, auto sandbox, hips, or viruscope so i assume the issue is in avast and it has to do with behavior shield. also i tried toggling commodo and avast on and off in many combinations and this is the only one that let me keep both.