Linux KDE startup problem

I’m running on Linux Redhat 7.1.I’m having trouble on starting my KDE and gnome after some
changes made on the TMP directory which i ‘m not sure what changes did i made.
Can you really advise me on how to get my KDE and GNOME running back with the little info that
i mention to you above,or can you suggest to me any website where i can really learn how to
troubleshoot Linux problem.At least does’t requires me to setup my linux redhat again.
Fed up with the installation again.