It does that everytime, and I run fsck (e2fsk) every time the crash occurs. It takes about 10 min fixing all the errors.
As I said in my first post, this kind of crash occurs when I had first a X-server crash, so to solve the problem, I guess I have to find why the X-server crashes in the first place.
I just hope it's not the hard drive. But since it's reproducible, i.e. not random, I guess it isn't. Somebody suggested I reinstall X...