Hello, I have an old Alienware, it could be Model X51, and it is from approximately 2015. a small skinny desktop shape. It turns on, with very loud fans, but I have pluged almost all video cables into it, and the screen is blank. The screen is always blank, the screen has always been completely blank, it does not work at all. I am using a well tested perfectly working monitor. I have tried both the GPU's HDMI & DVI, and also the onboard HDMI directly on the motherboard, but neither one displays anything. I have checked all cables are plugged in correctly. What are the next troubleshooting steps I should take? Thanks guys.