A lot of times there is an "INPUT" button on your remote that allows you to select which port to receive signal from.
I can plug multiple devices into the back of my TV like a USB stick or a ROKU device. Then when I hit the INPUT button it brings up a menu allowing me to select which signal to watch.
He's already mentioned switching the input of his TV to HDMI3, so he's done that. It would be nice to know:
a) What model his TV it is which is typically printed on the back of the TV. Taking a pic of that would provide that info.
b) be able to ensure the cable is in face installed correctly as well as what other input options are available with his TV. Taking a pic of the inputs that show the labels with the cable plugged in would provide that info.
c) What model his PC is. He should be able to pull up
System Information on his PC to figure that out. At least that's where it use to be. As I mentioned, I haven't used Windows in a very long time.
d) What is port setup on his PC is on both the front and the back. A pic would provide that info.
Given that info, we can figure out if he has it setup correctly, if the PC can output what the TV requires as input, and what needs to be done to configure Windows to output through USB, as well as what needs to be done to configure his TV to use whichever HDMI input he would like to use.
If his PC can output USB can convert that to USB using his adapter (which most modern PCs can), I think that would be preferred over using lower resolution outputs later converted to HDMI.