Try disabling your plugins and make sure you don’t have it set to minimize to the system tray.

http://sourceforge.net/p/notepad-plus/discussion/482781/thread/dbea5d02/?page=0
https://sites.google.com/site/fstellari/nppplugins
http://www40.zippyshare.com/v/rGAcMraC/file.html

@dail Wow you are totally right, i disable it and everything is fine now, thank you very much !!!

Biggest found by Google images : http://getkeystrap.io/img/notepad-logo.svg

and this happens when I open the file from explorer.
from the context menu of npp(File > Open) and from the explorer-plugin opens normally

True credit goes to guy038, but I’m glad I could assist.

I understand, that’s why I didn’t post this earlier: my current version is 6.8.3 and the latest release is 6.8.6, so it should at least update my software to 6.8.5. I’m wrong ?

Manual updates are perfectly fine and you don’t have to uninstall old versions.

I notice that in my"?" menu there is no check for updates

You either just have the standalone version of N++ (which does not auto-update) or during the installation you didn’t select the “automatically check for updates” option.

The auto updater is triggered about a week after a release, that way in case any major bugs are found, thousands of people don’t have a bad version.

Bugs can be reported on Github.