I've never heard of wifi box restricting devices but I'm no tech expert. Are you sure the password you input was correct? If the wifi box is the problem, can you replace it with your own wifi box? I'm with Xfinity, I have to use their internet router but I bought my own wifi device. Xfinity doesn't control or provide support for it.
There are two potential situations here:
Case 1:
You are trying to connect to the private wifi network that someone from optimum set up for your parents (I'm assuming they are not tech savvy) without the password.
If so - solution is easy. The wifi password (sometimes called "access code") will be written on the router itself. Use that, and you should be able to connect.
Case 2:
Optimum has a concept called "optimumwifi". They basically allow you to use publicly available wifi access points with your optimum username/password. It may be that the parent's router is advertising itself as a "optimumwifi" host, and that is what you may have been trying to access.
If I remember correctly, there are ways to tighten up your router to remove it from hosting an "optimumwifi" access point. AND obviously you should be able to connect to the private access point and not the public "optimumwifi" one.
How do I make all these guesses? Optimum and Frontier are the two internet providers in my area. I currently have Frontier, but I have also had optimum in the past.
Here is my topically relevant badassity thread I posted in the MMM forum itself:
https://forum.mrmoneymustache.com/share-your-badassity/reduced-my-cable-internet-tv-bill-from-$165month-to-$51month/[/quote]
I'm going to try to connect my desktop with an Ethernet cable first, and see what happens.
Just to reiterate: The Ethernet cable goes from my parents' router or modem directly into the back of my desktop tower. Nothing additional needed, right?