For disgrace I have asked advice in "chiedi Ubuntu" forum - the Italian version of ask Ubuntu - and for following their advice, I can't get anymore in my Ubuntu account due to internal errors of the operative system.
Basically, I have just entered these commands " sudo apt-get autoclean " and " sudo apt-get autoremove " (the reason was that my Ubuntu became too slow) but now after entering the password for accessing into my account, the operative system just stuck - as if it can't load properly.
They then suggested me to use Ubuntu live to save my data (I have important data inside my account) but I can't find the folder (I hope I have not lost them! But I think I haven't)...
In short, I have 2 problems: first, I want to be sure my data are ok and I would like to save them in an external support (also, I would like to recover the list of my favourites websites from the browser). Second, obviously I would like to enter my account (if I am successful in the first step, saving data, I can consider also to reinstall the operative system).
Maybe I was too long... but I hope I was clear!
Ps. I am writing here because they don't answer always and it is already days I can't solve this problem