Hi @charlespeti4062

Troubleshooting steps:

Have you checked/changed the batteries in the remote?

Use a digital camera or the camera app in a mobile phone to test if the remote is working OK.

Turn on the camera or open the camera app in the phone and then point the end of the remote, that is normally pointed at the projector, towards the camera lens so that it is visible in the LCD screen.

Press the Power button on the remote and you should see a light turn on at the end of the remote, when looking at the LCD screen.

If you don't, then try any other button and check.

If the light doesn't turn on when you press any button, try the test on another known working remote e.g. TV remote, to make sure that you're performing the test correctly.

If you still don't see the light when pressing any button on the remote, check that there's no button stuck down in the half operated position. If they appear to be all OK then the remote is faulty and would need to be opened and checked.

If you see a light on the remote when the Power button is pressed, then there's a problem in the projector.

Check that there's nothing blocking the projector's IR window from receiving the signal from the remote.

Here's the ifixit Optoma HD20 guide that may help, at least to gain access so that you can check if there's anything obviously wrong e.g. burnt out components etc.