The C:\Windows\Installer folder is a hidden Operating system folder.Caution
To view you would have to go to Tools, folder options, view, an untick Hide protected operating system files.
It is hidden for a reason and is not recommended to be manually altered.
Manually altering the contents can cause programs updaters/uninstallers to malfunction or cease.
Regarding failed uninstall/re-install download a copy of CIS here
and then try the unofficial Uninstaller Tool for Comodo Products
before attempting re-install.