I have tried many things including the installation of gMTP from Ubuntu's PPA, and with it many other that include mtp-dev... I have forgotten now the bunch of files I have installed.

The problem is that when I plug my S3mini into my computer it is not recognized, however if I change the way of connecting form MTP to PPT (I believe is PPT the other way) it does connect, and if I go back to MTP again it does connect. The problem is that I cannot move big files from and into my cellphone's internal storage.

I know and I use Airdroid for small files, I have Dropbox but my internet is limited and slow, and both options (Airdroid and Dropbox) take years in copying a movie onto the cellphone.