Yesterday my computer suddenly went wireless. How do I change it back to modem/router only? If it's any help my router is a model MI424WR. I can't find any info online and I'm technically challenged.
I would verify that your wired conncection on your computer is active. IF you do not use wireless it can be turned off on your PC or laptop.
Please post the Operating System (Windows & version or MAC) on the computer and tell us if you ever need to use wireless (such as a laptop used in a coffee shop)
As Jose said, Check the ethernect connection! Most computers will default to ethernet if it's available. Try changing the port on the router and make sure your ethernet adapter is active and the drivers are working.