Q: Macbook Pro shuts down after entering password.

Hi there hthrrh,

As I understand, your MacBook Pro on Yosemite is shutting down after you enter the password and apparently isn't showing any screens to give you an indication of what's happening. It's always hard to know what the best solution is when there's nothing to go on. I'll be glad to provide some troubleshooting steps to get your MacBook Pro working as it should again.

The first step to try is using Safe Mode -- Try safe mode if your Mac doesn‘t finish starting up
 

Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks, and prevents some software from automatically loading or opening. Starting your Mac in safe mode does the following:

 

• Verifies your startup disk, and attempts to repair directory issues if needed
• Loads only required kernel extensions
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts 
• Deletes font caches, Kernel cache and other system cache files
• Together, these changes can help resolve or isolate issues related to your startup disk. 

If your MacBook Pro still won't go past the password, check to make sure that your hard drive is is working correctly by running Disk Utility while in Recovery Mode and repairing it if needed. -- OS X: About OS X Recovery 

This will bring up OS X Utilities. Select "Disk Utility" in the first window window and run First Aid. If any problems are reported, repair the disk -- Using Disk Utility to verify or repair disks

It may be that you need to reinstall the operating system if the above hasn't corrected the issue. -- How to reinstall OS X on your Mac

Take care!