@hugadog I'm assuming that the HDMI cable has been plugged into the GTX 1660Ti graphics card, not into the motherboard HDMI connector. Therefore, I'd suggest the following:
- Turn off the computer, open the case and remove the graphics card.
- Plug your monitor into the motherboard HDMI socket.
- re-boot your PC.
If this works, then the fault is probably with the graphics card.