This is a common problem whenever a Linux mismatches the video driver or the screen scanning frequencies.
Linux operates on generic drivers for the monitors and video cards. If the one you have isn't listed then Linux will try its best to run a setting it thinks best fit your situation.
The problem can be easily cured if you know what sort of Linux standard driver will work for your video card and edit the scanning frequencies to match those provided by the manufacturer.
Remember you don't supply a driver in running Linux but you need to try a few drivers to get the best result.
I think you may be able to run the X-windows configurator in Slax terminal mode. Try this command
The error of the Xorg is listed in /var/log/Xorg.0.log
The xorg cinfiguration is in /etc/X11/xorg.conf which is a text file you can edit
The drivers are stored in /usr/X11R6/lib/modules/drivers or
Once you have edited the xorg.conf, save the file and try "startx" again until it works.