|Can you help clearify. It sounds like you have two problems.|
1) The system shuts down
2) The laptop will not switch back to the main screen and only works with external monitors
1) When does the system shut down? Are you able to get Windows fully loaded and it shuts down at random times or does Windows never load?
2) I think that computer comes with an ATI card which has a Crystal Control Center (CCC). I have uninstaled on my laptops because I had such trouble with it. You may want to uninstall it and see if it helps. You can always reinstall it latter.