Start up Macbook Pr
After the latest OS X 10.10. 4 and ITunes updates, I have had a problem on startup I sign in but the startup bar only moves a quarter of the way across and there it stays until I shut down and start again same happens but a box says you shut down because of a problem, I press continue and it then starts up fine. Any ideas, macbook pro is about two&half yrs old. I have cleared any start up programs that may have been causing a problem. Thanks for your help.
Mac Pro, OS X Mountain Lion (10.8.3)