Looks like you are complete newbie
Press ctrl - alt- F1 and login as root.
#> init 3
#> cp /etc/X11/xorg.conf /etc/X11/xorg.conf_BACKUP
Hope you know to use vi - editor
#> vi /etc/X11/xorg.conf
Go to: Section "Screen"
Now go to the line:
Go to Subsection "Display"
change the Modes line:
Modes "1280x800" "1024x768" "800x600" "640x480"
Change the values based on your laptop screen.
Save the file. Now as root
#> init 5
wait a few seconds. you will have correct desktop.
(Remember changing your screen to a wrong values *may* damage the screen)
It would be good if you join your local LUG Linux users group.