KDE doesn't work after driver install

[windwos]

Ok I probably messed something up:

I used YOU to install the driver, as the HOWTO said I would. One thing I totally forgot, which I saw now, was that I was supposed to mark it as an update. I just checked the box and continued.
Is that the problem?
Because now after that blue thingy with the hardrive, keys, some card and a system, it comes to the, what's it called?, the "code place".
I've tried "exec kde" and "exec startkde" but it gives me:
xset: unable to open display ****
and some other errors.

Can this be fixed? Is it really the update miss behind all this?
I installed the nforce drivers just before that and they worked, so I guess my kernel is okey.

edit: I just reinstalled everything, forget it.