Windows 7 home premium logon failure

Long shot but anyone know how to access a laptop that won't let you log on to your user profile any more?

You get the welcome screen but when you put your password in and press enter it gets you all excited because it briefly says

Welcome

Then it says

The User Profile Service service failed the logon

User Profile cannot be loaded.

Any ideas how to get in to Safe Mode?  I have tried all the F keys

Here's hoping.

Thanks