If your Roku Express is seeing your network (but just not connecting to internet), you can try seeing if you can place the Express on your other TV and get different results, or try connecting to a hotspot (for testing) and see if the Express can connect.
You didn't mention what your other Roku device is. The Express will only work on the 2.4gz network band of your wifi so you may have to adjust the channel or bandwidth settings in your router settings in order to get a stronger signal to the Express. You did mention the Express is in the basement. Possibility that the channel assigned in the router has too much interference and hindering the signal to the Express, or the Express may be too far from the router to get a good signal.
Post back if any of the above helps or you are still having issues.
