when the X fails to start, I presume you can login using the shell?
do this as root and start YAST (I guess it's just typing "yast" at the prompt, but it's been some time since I last used suse) ... you will then get the yast configuration/install 'environment'
(looks a bit the same as in X)
go to the settings of your monitor and video card, try to reconfigure it there (maybe your monitor settings changed because of the installation of new drivers???) ... and see if it works then (after shutting down yast, type "startx" at the prompt).