M14x R1 running with LCD-Screen disassembled possible? - 8 beep

Dear Community,

First of all: Thank you all for helping me out so often. Until today I was a reader only. This is my first post.

Today I did a complete teardown of my m14x R1 in order to remove the built in LCD-Screen including the housing. I removed the cables directly from the motherboard. The 2 following ones (picture) and also the WiFi cables on the bottom side:

Now it looks like this:

The hinges of the monitor were broken and as I don't use the built-in screen anyways I thought running it with an external monitor only would be a good idea.

But unfortunately it doesn`t work. After connecting the "naked" laptop to an external monitor and pressing the powerbutton it takes a few seconds, then I hear 8 beeps.

Following table from the forum tells me "LCD" -problem.

Alienware Beep Codes Table 

 Laptops
1 Possible Motherboard (covers BIOS corruption or ROM error)
2 No RAM detected 
3 Possible Motherboard Chipset
4 RAM failure (other)
5 CMOS Battery
6 Video card/chip
7 CPU
8 LCD 

My questions to you:

Does the m14x let me run it with the internal LCD disassembled?

Is there any check of the motherboard if the original screen is connected? 

Or did I accidentally break something and the 8 beep means "video-card broken"?

Before buying new hinges and doing the whole disassembly and assembly again I would be very happy if someone can help me

Thank you very much in advance!

Jan