I have a non-working copy of Logos 4. What happened with me is following:
a) downloaded Logos 4 setup.exe - installed it
b) Indexer started and crashed, but the main interface did start, with no content - there was some status icon saying the library is being indexed. But I could not wait and exited.
c) Now the interface doesn't start at all. Each time it says it crashed and want to report to Microsoft :-) I reported it.
d) I tried reinstalling Logos (did not uninstall pre-requisites, though), but the same result (the Indexer didn't even appear).
How to make a clean uninstall of Logos 4? Which .Net version is required for Logos 4? Perhaps, some old versions of .Net are hindering the work?