==== ROOT does not start/work, or prints error messages about missing/wrong shared libraries during startup =====

Please remove or rename the files `.rootrc` and `rootlogon.C` in your home directory and the current working directory, and also make sure that the environment variables `LD_LIBRARY_PATH` and `LD_PRELOAD` are unset or at least definitely point to the right shared objects for the ROOT version you're using. If ROOT now works normally, you'll have to find out what in your startup files is causing this behaviour, or why your environment variables point to the wring shared libraries.