Kryptview a780 setup problems

If you have reset your router, and ensured Mac Address filtering is disabled, then I can not think of another default router setting that would give this problem.
But one thing is for sure, if your box works with a direct ethernet cable attached to the box from your VM modem, then it all points to the router or ethernet cables somehow. And your router is not to old to do the job at all.

With the same set up, do you have a problem with a wired connection from the router to a desktop\laptop if you switch off the desktops\laptops wireless?

I am not saying buy another router, but if you can get your hands on another one of a friend just to try, it would help to clarify things.