You probably have a shell extensions that is crashing or locking up.
Crash, exit or high CPU when right-clicking certain files has instructions on how to track down the cause of problems like the one you're seeing.
Also check that your Notepad++ is the latest version as an old version caused lots of problems with the right-click menus, and for some reason a lot of people are still using that version today, even though it's years old and was fixed very quickly by the authors. (I'm guessing the old version comes bundled with something else, or is still being linked to by a popular site or something.)