DELL LATITUDE E6440 not powering on (No POST)

Dell Lattitiude E6440 won't start when I try to power on. The power button will light up few a few seconds, then go out. The first light (hard drive) will remain flashing, while the other 2 remain solid; yet the power light is off. It sounds like the fan runs for a second to get it to boot but then it just stops. I've replaced the motherboard and CPU and am still getting the exact same response. I've tried using different RAM, unplugging the battery from both the laptop and the motherboard and resetting the power, and even tried removing the LCD monitor and connecting to a separate monitor through VGA. All still giving me the same issue. If anyone has any other ideas or thoughts on how to get this laptop running please let me know! Help is greatly appreciated!