How can I recover if built-in laptop monitor and external monitor isn't working?

Question

My laptop's built-in monitor is already broken. So, I tried to use an HDMI cable to connect to an external monitor, and it displayed and worked without any problems for few hours. I had to restart the system few times, restarted and logged in multiple times. All done through external monitor. Everything was fine then.

Later, for some ergonomic adjustments, I disconnected all cables and devices connected to the monitor and laptop. After adjustments were done, reconnected everything, and external monitor isn't detecting HDMI connection with laptop. External monitor shows "No Signal" even when the laptop is connected. A usual connection that worked just few hours before is not working now.

What are the possibilities that I could try out in this case?

I tried resetting external monitor. But no luck.

Note:

1. Can't do anything terminal-related as built-in monitor is useless and not displaying anything.
2. While it was working, I changed primary display to HDMI output in Display Settings as I needed the system to connect to the HDMI output from now on by default.

Operating system is Manjaro Linux.

External monitor is LG and has both HDMI and VGA ports.

Laptop is HP, no VGA port, instead, only HDMI.

Answer 1

Do you have access to another computer on the same network?

If so you could either

1) ssh into it from there to inspect config files and log files
2) unscrew the harddrive and connect it to another computer and inspect config files and log files

Furthermore, in my experience both HDMI and laptop's internal monitor both show output during boot. It's not until the graphical environment starts up that graphical output gets specific.

If you need help finding the IP to connect to from the other computer, nmap -p 22 192.168.0.0/24 should do the trick (substitute for your LAN IP range)