I had the same two problems.
What helped me with the resolution was:
go in terminal mode (e.g. ctrl+alt+f1)
stop kde with: service kdebase stop
then in the directory /etc/X11
rename your original xorg.conf (so you can restore again, if this does not work)
(this detects now your hardware)
after that in your xorg.conf change
in: Section "Screen"
change Modes and Depth as you wish
service kdebase start
and now I wish you all luck :-)