If your monitor shows no signal through the Aluminum Type-C to HDMI Adapter (ST-TC4KHAS, ST-TC4KHAG, ST-TC4KHAM, and ST-TC4KHAR), the usual cause is a USB-C port on your computer that does not carry video. The Aluminum Type-C to HDMI Adapter outputs video up to 4K at 60Hz and is plug and play with no drivers required on macOS or Windows, but the USB-C or Thunderbolt port you plug it into has to support DisplayPort Alt Mode (DP Alt Mode). Work through the steps below in order.

Steps to fix the display on the Aluminum Type-C to HDMI Adapter

1. Make sure the USB-C connector on the Aluminum Type-C to HDMI Adapter is fully seated in your computer's USB-C or Thunderbolt port.
2. Confirm the USB-C port on your computer supports DisplayPort Alt Mode (DP Alt Mode). Not every USB-C port carries video, so check your computer's specifications.
3. Check the LED indicator on the adapter, which illuminates when the Aluminum Type-C to HDMI Adapter is connected and active.
4. Switch your monitor, TV, or projector to the correct HDMI input source.
5. Use a direct HDMI to HDMI connection to a display that has an HDMI port. An HDMI 2.0 cable is recommended, and the Aluminum Type-C to HDMI Adapter is backwards compatible with HDMI 1.4 and up.
6. Keep the resolution at or below 4K at 60Hz, which is the maximum the Aluminum Type-C to HDMI Adapter supports.
7. Try a different HDMI cable, then connect the monitor directly to your computer to confirm the monitor itself works.
8. Try a different USB-C or Thunderbolt port on the computer, and disconnect and reconnect the adapter.
9. On a Mac, open System Settings, go to Displays, then hold the Option key and click Detect Displays. On Windows, open Settings, then System, then Display.
10. Install any pending operating system updates, then reconnect the Aluminum Type-C to HDMI Adapter.