yosemite install complete but now i get a white screen with grey apple and bar then n

[m18mpa]

Hi guys,

A bit late installing Yosemite as I've been travelling and when I ran the update last night it completed and then my MacBook restarted. When restarting it came up with the white screen, grey apple logo and a loading bar. When the bar gets to the end after about 15 minutes the MacBook just shuts down. So I restart it and it does the same process. Tried and tried but nothing. Any ideas?

Thank you

 

[Apple_Robert]

Try booting into Safe mode. If that doesn't work, you could have a bad HD.