Ralston18 :
Not sure but there may be a way to see what is happening.
You have found a pattern, i.e.:
"I think it actually won't boot at all without external monitor, because if I push power button and THEN connect external monitor nothing will happen. I must connect external monitor BEFORE turning on my laptop."
Clear the Event Viewer logs.
Turn on the lapton then connect the external monitor - the "nothing happens" scenerio. Turn laptop off, connect the external monitor, power it up, and restart the laptop and see the display.
Check the Event Viewer logs. See if there is some log entry related to the post-connection (after start) attempt and then some difference in the entries when you connect the external monitor before starting.
You may also be able to look at Task Manager via the laptop's screen. Look for some process or service that fails to run or start when the monitor is or is not powered up.
Could be just that the combination of hardware, software, and configuration does not support or otherwise accomodate Plug and Play when the monitor is connected after start up. Getting the monitor to display depends on the monitor being powered up and detectable beforehand in order to have the process work. Or there may be some software bug preventing that from happening.
Will admit I am not sure about the specific causes involved but it does seem that there are still some trouble-shooting options available. Just need to methodically grind through it all.
In Event Viewer I can see:
-Warning: 'Kernel-PnP' saying: The driver \Driver\WudfRd failed to load for the device ROOT\WPD\0000.
-Warning: 'DNS Client Events' saying: Name resolution for the name gfwsl.geforce.com timed out after none of the configured DNS servers responded.
-Error: 'DistributedCOM' saying: The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
{6B3B8D23-FA8D-40B9-8DBD-B950333E2C52}
and APPID
{4839DDB7-58C2-48F5-8283-E1D1807D0D7D}
to the user NT AUTHORITY\LOCAL SERVICE SID (S-1-5-19) from address LocalHost (Using LRPC) running in the application container Unavailable SID (Unavailable). This security permission can be modified using the Component Services administrative tool.
-Error: (again same DistributedCOM)
-Warning: 'DNS Client Events' saying: Name resolution for the name stats.mbamupdates.com timed out after none of the configured DNS servers responded.
-Error: (again same DistributedCOM)
All errors and warnings are at almost the same time (when failing to power on my laptop) except last 'DistributedCOM' error. It is about 30 seconds later.
I had a similar problem few months ago... It was actually the same problem like this one, but it only happened when there is a CD in my laptop, and when I click power button, I can open the CD drive, and then I restart my laptop without a CD inside and it works normally.
I didn't actually understand that part about Task Manager... Where should I look when I open Task Manager?