When I compare two text files with Notepad++ 5.8.2 Compare Plugin 18.104.22.168 on my Windows 7 64-bit system, the result is a repeated flashing screen.
The only way out is to force a system shutdown via Ctrl-Alt-Del. Even this is not easy, if you have any unsaved files.
It would seem that the fact my system is the 64-bit version of Windows 7 may be the significant circumstance here.
The symptom does not occur on the 32-bit version of Windows 7.