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. 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.