Cannot setup Drupal anymore
It could be write permissions of the files - try chmod -R a+rw . command in Terminal in the root of your drupal folder. It could be a time out meaning that the database is not been written correctly (don't have a remedy for that, except for not using a native setup, but rather a Virtual Machine, VM-based setup...)

You might want to consider a VM-based setup (which would more closely resemble your production environment), see a guide I wrote to using Vagrant to automate generation of a setup here: https://stackoverflow.com/a/15067918/227926