That means the screen is OK -- leaving the mainboard as the part to replace. [URL]  
I'm trying to fix a friend's 5540. When i power it up nothing shows on the screen, only the power button lights up. I tried replacing the ram, and unplugged everything i could(battery, SSD, cd drive). The only thing I can do is when i press the key D on initial boot it will cycle colors on the screen, like a diagnostic. 
Dell latitude e5540 no image