Vista - Black screen with a mouse cursor after logon

Hello,

something screwed up badly in my system so I can't use it. It boot properly,
I can get to the logon screen, there I can put my password and everything
seems normal till now, but then the screen goes black with only a mouse
cursor displayed (I can move it), the system is obviously (harddisc active)
starting up, but nothing is visible except the mouse cursor.

I can use CtrlAltDel to get to the menu where I can log off or turn off
computer without problem, but if I choose Task Manager, I get the black
screen again.

The same problem under safe mode, 640x480 VGA mode etc. I tried to restore
from last restore point, but that point was the only one made and was created
just before all of this happened to me and restoring it didn't help.

Please, does anybody know anything about this issue? Some advice?

Thank in advance.