If, i think, i hope, there should be a way to reset the system back to siduction like without deleting it, isn't it?
Sure -- the only thing that is needed is the list of every change made to the default configuration of your system. :roll:
You can lose a lot of time chasing mysteries on a system of unknown configuration -- it's your computer, maybe you can back out enough, and replace enough, to get it working normally. The problem is, you can never really be certain. Then the next time something unexpected happens, you are doomed to wonder about the non-standard bits that you thought you fixed.
A reinstallation of the OS, on a machine with a separate partition for /home, takes only a few minutes, plus some updating and configuration time. For sure you can have everything that you have now in a couple of hours, and no future questions about mystery breakages.