Unplug the system, disconnect the battery from the system board and hold the power button.  Re-check that the keyboard cable(s) is (are) firmly seated.

Then try powering up again.

Did you disconnect the battery when replacing the keyboard the first time around?

Hi @Zmw2021  welcome to this user to user discussion forum. This is not Dell Support. 

Having replaced the keyboard, was the original Dell part number label stuck on its underside, identical to that on the replacement keyboard? Check to see if key combination fn + f6 will increase screen illumination. 

To see if LCD screen works:-  
1. Turn off the computer. 
2. Disconnect any external devices that are connected to the computer. 
3. Connect the ac adapter to the computer. 
4. Press and hold down the D key, then press Power-on button to enter LCD built-in self-test (BIST) mode. 
5. Continue to hold down the D key, until you see colour bars on the LCD screen. 

If screen test fails, connect an external monitor or TV, so that the the external screen shows what should be on the computer screen. Shine a light oblique (at an angle) to the computer screen, if a very faint image is detected, the screen backlight is not working. 

The Procedure and Post-requisites for Replacing the keyboard, also includes automatic refresh of the POST instructions for hardware checks, but this is undertaken during Boot. So it is possible that the POST diagnostic lights and beeps will disappear when the system boots, but boot did not happen. Connect the internet cable to the system (because WiFi might not be working). Keep trying to power-on the system, assuming that the screen is working, this should get the windows recovery window to appear. 

What to do next, depends on what system capabilities are now available. 

Please click on Kudos to say thank you for response from another user. Please share an update on progress, so that other users derive benefit from your experience. Thank you. 

to get to the keyboard you must strip the entire machine as it sits below the mother board so yes all compontents were removed but my gpu was never working with onboard lcd the back lid of the lcd was not working due to the gpu but hdmi was once i replaced the keyboard and tried to power it the response from gpu totally gone

Hi @Zmw2021  thank you for sharing update.  I do not have an Area-51m, and can only speculate on the information provided in the OP.  @DELL-Chris M 

The Area-51m System diagnostic lights and the actual POST diagnostic lights from the Power-on button >> from green to red to light blue then bleeps, are not easy to interpret because three different system diagnostic light colours are not explained. There must be two sets of repeating colours, and the first set must be either 2 or 3 identical colours. Ignoring the colours, Light Pattern 2,1 = CPU failure. If POST diagnostic says there is a critical hardware fault, computer will not Boot.

Dell Beep Codes are not listed for the Alienware series, but for other systems, a single beep = Motherboard: BIOS corruption or ROM failure.

Getting the screen to work is a must for F12 ePSA Diagnostics to run and to reveal test results. 

I tried this for 2 days straight my backs destroyed trying to fix this machine.

some months ago the machine lost its back lid lighting on the lcd so I thought my lcd is dead I bought a brand néw lcd for the 51m after I replaced the screen still same issue then I thought my gpu might be the issue I got it re heated by a professional tech and for 6 months all well no back lid issues... recently it started doing same thing so I used hdmi now I got new keyboard replaced it when I on the pc it does 2 green lights then 1 red light then goes into beep mode I have removed the gpu ready to order new one but I can post the digonistics without gpu if u can figure out what hardware is dead I don’t want to order gpu and then cpu or mother board is dead cause then I just loose total of 750 for nothing if gpu doesn’t work

Sorry my second acc I couldn’t find logins to this one strangely was saved on my other phone so posted of it 

Hi @Zainmw91  thank you for sharing update, from your other Dell account. 

It is not easy to determine what fault is causing this problem. The POST process is working, so the Area-51m is not technically dead, it just will not Boot until the POST tests have finished checking all the hardware, but it is trapped in a loop. . 

Please reseat the OS(C:) drive. If your computer can't load an operating system, because it doesn't detect a bootable drive, it will usually pause, beep and give you the option to enter the BIOS, which it will often call "setup". But your screen is not working, so the POST testing of hardware, just did not get around to test the video card(s). If backup clone OS(C:) drive has been created, or there is an original OS(C:) drive, swap this in.  

Keep pressing and holding down the F2 key during power-on, perhaps it will provide the BIOS window. 

Hi @Zainmw91  thank you for sharing update. 

Seems there is life in the Area-51m and with RAM card change, it reluctantly allowed F2 entry into BIOS with the screen working. This is good. If you can work the same magic, press and hold down F12 to run ePSA Diagnostics to confirm the hardware problem. 

Well this test is no more possible as gpu gives 0 output but in the past 2 days of diagnostics it booted twice with ram stick in sim 1 slot once it booted I packed it up completely it died I re opened and second time it booted via hdmi I went in the bios settings to make the onboard gpu as primary but that was not a option seems like the open gpu is just to accelerate the form factor gpu for now no digonostics can be made due to the gpu. But mobo and process look good for sure gpu is dead not sure if my ram sticks or slots are effected this a worry if not I think by replacing gpu it should come back to life.

without the gpu it one 2 green lights then one red light then beeping mode that’s all.

I am guessing the ram must be configure in sequence so 1 2 3 4 

or can it be 3 4 

I guess I will risk it and go ahead with a new gpu 

So everything works fine. just a GPU being dead. Heres one on eBay but its a 2070. Alienware Area 51M RTX 2070 Nvidia Video Card 8GB N18E-G2-A1 Dell PV1GD | eBay

Hi @Zainmw91 having F2 entered BIOS MAIN tab to look at Integrated and Discrete graphics on the Area-51m, there should be:-
(1) Integrated graphics (GPU) to say what came with the CPU, and
(2) Discrete graphics (GPU) to say a graphics card has been installed.
The ePSA Diagnostics test will then say if both graphics are functioning. 

Without the Discrete GPU card, POST diagnostics are two green lights then one red light, Light Pattern 2,1 = CPU failure. 

Without the gpu this is what happens 2 green then 1 red I have removed the gpu and send it for replacement should get one in 2 weeks hopefully I will post back once I have it

I can’t buy the 2070 or the 2080 cause I bought the 2060 for it and the higher versions need a totally new heat module for it to work with 2070 and 2080 so sadly only way out is to buy from dell  

I actually searched everywhere online for the 2060 no1 on the internet sells it 

Not sure if this will help, but you can actually unplug the DGFF GPU from power, there is a powewr connector that goes from the GPU to the board.  Then you can use a USB-C to HDMI cable and run off the iGPU.  I have done this with an Area51m-R1 9900k/2080 variant and it works.  This might at least get it booting and somewhat usable for now.