Area-51m R1, display issues

Hi Guys,

I am hoping some of you can help me i have a issue with my display... The first display i got worked for almost 9 months before it just started flickering when i rang up dell the lady told me if i connect my laptop to a external monitor and works fine without any flickering etc this means my gpu is fine so i did and used it on a external monitor for almost 3 weeks in the mean time i ordered a brand dell alienware 51m Screen from ebay  since i am out of warranty (The purchased 1 year warranty expired on April 12, 2020) i got it today i replaced it with the old screen first 20 mins everything looked prefect no issues screen working fine.

After 20 mins 1 side of the LCD just went black dim i had a slight idea what it could be i felt maybe the machine is to hot so i put it under a fan to cool it down after good 30 mins when machine was cool i booted it up and lcd is fine.

I am guessing my gpu is either gone or i need to re-paste it could some of you advise what steps to take to find the issue if there was cable issues it would have never worked the first 20 mins fine or even now as i type.

So i would be great ful if you guys can help me out i spend alot of money on this laptop its just been problem 

Thanks in advance