there is some things you have to do to start kde heres a quick howto
sets in make.conf
INPUT_DEVICES="keyboard mouse evdev"
VIDEO_CARDS="your gpu-card" (google=gentoo howto xorg)
emerge xorg-server
emerge kdebase-startkde or emerge kdebase-meta or emerge kde-meta (light,medium,bigass=your 12 hours)
rc-update add hald default
rc-update add dbus default
if you running as root.
nano -w /etc/X11/xinit/xinitrc.
set a new first line with exec startkde
this is the things you have to do to start kde
if it dot work with this its your gpu-card settings that fails
type nano -w /var/log/Xorg.0.log
and send the lines that starts with (ww)
Check this too
The X Server Configuration How To