cat ~/.xsession-errors
Post the output. And, have you recently changed the video driver?
Output for cat ~/.xsession-errors is:
[hugo@localhost ~]$ cat ~/.xsession-errors
/etc/X11/gdm/Xsession: Beginning session setup...
/etc/X11/gdm/Xsession: Setup done, will execute: /usr/bin/ssh-agent -- /usr/share/X11/xdm/Xsession default
/home/hugo/.Xresources:1: warning: End of input with no newline, supplemented newline
Xft.lcdfilter: lcddefault
Failed to connect to the VirtualBox kernel service
Failed to connect to the VirtualBox kernel service
Failed to connect to the VirtualBox kernel service
Failed to connect to the VirtualBox kernel service
localhost being added to access control list
hotkeys: You must set the keyboard type, use hotkeys -t <type> to set it.
s2u: symbol lookup error: /usr/lib/libnotify.so.1: undefined symbol: gtk_status_icon_get_geometry
Obt-Message: Xinerama extension is not present on the server
which: no hsetroot in (/bin:/usr/bin:/usr/local/bin:/usr/games:/usr/lib/qt4/bin:/home/hugo/bin)
which: no esetroot in (/bin:/usr/bin:/usr/local/bin:/usr/games:/usr/lib/qt4/bin:/home/hugo/bin)
** (parcellite:3513): WARNING **: Binding '<Ctrl><Alt>A' failed!
Gtk-Message: (for origin information, set GTK_DEBUG): failed to retrieve property `GtkTreeView::odd-row-color' of type `GdkColor' from rc file value "((GString*) 0x8ba8e00)" of type `GString'
** (pcmanfm:3497): DEBUG: line = /home/hugo
** (pcmanfm:3497): DEBUG: line = 0
** (pcmanfm:3497): DEBUG: line = --show-pref
** (pcmanfm:3497): DEBUG: line = 0
** (pcmanfm:3497): DEBUG: FmJob error: No existe el fichero o el directorio
** (pcmanfm:3497): DEBUG: unable to load icon . GThemedIcon application-octet-stream gnome-mime-application-octet-stream application-x-generic
** (pcmanfm:3497): DEBUG: FmJob error: No existe el fichero o el directorio
** (pcmanfm:3497): DEBUG: FmJob error: No existe el fichero o el directorio
** (pcmanfm:3497): DEBUG: launch command: <gedit 'file:///home/hugo/Documents/hardinfo_report.txt' >
** (pcmanfm:3497): DEBUG: sn_id = pcmanfm-3497-localhost-gedit-0_TIME199306
** (pcmanfm:3497): DEBUG: vol-changed
** (pcmanfm:3497): DEBUG: vol-changed
** (pcmanfm:3497): DEBUG: on_mount_action_finished
** (pcmanfm:3497): DEBUG: mount path: disk
** (pcmanfm:3497): DEBUG: launch command: <libreoffice3.4 --writer 'file:///media/disk/home/hugo/Documents/Problema%20Video%20Openbox.doc' >
** (pcmanfm:3497): DEBUG: sn_id = pcmanfm-3497-localhost-libreoffice3.4-1_TIME253067
Gtk-Message: (for origin information, set GTK_DEBUG): failed to retrieve property `GtkTreeView::odd-row-color' of type `GdkColor' from rc file value "((GString*) 0xb186a840)" of type `GString'
[hugo@localhost ~]$
Translation for "No existe el fichero o el directorio" is "File or Directory does not exist"
Also, I haven't changed video driver.