|Buy a SOHO Router with 4 LAN ports. Connect it to your internet via it's WAN port and set it up as per the setup guide that comes with it. Then connect your other equipment to the LAN ports.|
You may need to contact your ISP when connecting the router in order to get everything working properly. From the sounds of it, your provider has registered the MAC address of the computer that does work and when you plug anything else in, it doesn't work because they have the wrong MAC address. If you know what you're doing, you can change the WAN MAC of your SOHO Router to be the same as the MAC of the computer you've been using that works.
If you don't know how to do that, call your ISP and they'll register the MAC of the router to the connection.
The advantage of the router is having multiple devices all connected at the same time and accessing the internet together. Also, it provides a firewall to help protect you and your equipment.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.