Monitor or TV? Thinking TV but best to confirm. Make and model?
Power "button" actually a red LED to show that power is available - correct?
Any pops or snaps noted during the HDMI cable swap; i.e., static discharge into the HDMI port?
What was the HDMI cable plugged into on the other end?
Do you have the applicable User Guide/Manual?
May be some troubleshooting options listed therein.
Overall, a few more details are needed. Thanks.