Creo Parametric 6.0.6.0 hang on launch and not responding

If you have a Windchill server connected, try removing or renaming the Windchill cache directory.  By default this is %appdata%\PTC\ProENGINEER\Wildfire\.wf, but you may have it defined elsewhere.  Just note that this will clear any saved work in your workspace that has not yet been uploaded.  That's why I always recommend renaming rather than removing, so you can recover the data if needed.