I just installed Suse 8.1, and everything was fine, I was in the YasT configuration screen, configuring the videocard and monitor, and when I clicked on test.. the screen when black, and I let it like that for about 4 minutes, and then I reset it.. and when I power it up again.. and when into linux, the creen whent black again... and thats all I got.. I put the boot CD, and I don`t remember wich option I click on, but after looking arround, I could finaly get into KDE... in KDE, I move settings, but when I boot up, I couln`t log in.... again.. and now I can`t get into it...

can someone help me with that??

in text mode, I typed startx, but nothing happend...

Most likely you hosed your /etc/X11/XF86Config file.
Not sure about SuSe, but try:
/usr/X11/bin/xf86config (this is a tool to reconfigure xfree86)
as root.
You'll need to know your video driver and monitors horiz. and vertical sync rates.