Check Windows Defender first.
Also check any antivirus or security products you have which may block things. Or tools like Autoruns which can disable startup programs.
Since the blocks are implemented by individual tools, and I don't know which tools you may have on your system, I can't give exact instructions as it will vary depending on what is blocking it.
(This is assuming something is blocking it. It might not be.)
Another possible cause of the problem is that you are running Opus as administrator (i.e. elevated via UAC). You should not do that; instead, use Opus's Admin Mode. Details here.