Cannot logon as user

[Vicky]

Hi,

I cannot login to either Gnome or KDE (or even IceWM) and i keep
getting this error message as soon as I login.

"GDM could not write to your authorization file.  This could mean that you 
are out of disk space or that your home directory could not be opened for 
writing.  In any case, it is not possible to log in.  Please contact your 
system administrator"

However, I can login and use the computer with no problems as Root.
Any suggestions or things that I can try out?

Regards

Vicky