My opinion is try to select Xterm in the Sessions at bootup and start some
programs at the command prompt to see what happens
Someting like:

firefox

Then try to use it, then close it down

ooffice -writer

Try to use it, then close it down

Then install some other WM or DE or install several WMs or DEs, lof out from
xterm, select another DE, log into it, try to use it, if it is fully functional
then it is OK, log out, select another DE or WM, log into it, try to use it, if
it can be used it is OK.