Hi Ngoko, that sounds frustrating.

I hope we can helop. May I ask you a couple of favors, please?
First, please do not double post. Just make one thread.
Second, although it does not directly address this problem, are you able to upgrade to 10.4.3, perhaps by using the Apple Software Updater program (from the Apple menu)? 10.4.3 is sooo much more stable than 10.4.2.
Third, if you can launch either the Terminal or the Activity Monitor (both in Applications/Utilities, I think), then can you please try *ONE* of the three following ideas:
1) Open Terminal, type "killall Dock" (no quotes, but use the same capitalization shown) and press enter. The Dock, Dashboard, and Exposé will temporarily be disabled, and will return in about five seconds. See if things work after that.
2) Open Activity Monitor, type "Dock" in the search bar. It will come up with the dock process. Highlight it, and click the Quit Process button, and confirm if you are asked to do so. Again, the Dock, Dashboard, and Exposé will temporarily be disabled, and will return in about five seconds. See if things work after that.
3) If neither of these work, go to the Apple Menu, then Force Quit. Select finder from the list. The Force Quit button will change to "Relaunch Finder." Click it.
Please see if any of these three help you?