Q: slow start up, then shortly after reaching the desktop, shuts down

Hi, Gerald Fluhrer.  

Thank you for visiting Apple Support Communities.

I understand that your MacBook Pro restarts unexpectedly upon reaching your desktop.  I would recommend going through the troubleshooting steps in the article below when experiencing this issue.  

OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem."

-Jason H.