I think you need to set the correct horizontal and vertical refresh values for your laptop's monitor and that should fix your problem. You can do this in "dpkg-reconfigure xserver-xfree86" if you choose the "advanced" monitor configuration.
The correct monitor refresh values you should find from the manual that came with your laptop. If the laptop didn't come with a manual or if you've lost it, then you can try installing a hardware probe tool called xdebconfigurator (aptitude --with-recommends install xdebconfigurator). It's far from foolproof but in many cases that's your best available option, so it might be worth trying.
After installing xdebconfigurator, you can "su" to become root and then run the following command:
xdebconfigurator -x
This should output a list of probed info about your display hardware and you can use this info in "dpkg-reconfigure xserver-xfree86".