Based on the owners manual for the 1900, it states that "fast blink" of the LED which is what I "think" we are seeing there indicates that it is "waiting for output voltages to stabilize before turning on CarPC". I'm assuming the PC is a laptop based on the use of the 1900, so that would explain why the PC started in the first place then shutdown right away probably due to low internal battery voltage.
So if the above is correct, I would suggest you check the red then yellow across the black ground input power wires for BAT+ voltage. Then check the output voltage for whatever you have the suppy set to via jumpers. Also check the small red 10a fuse inside the supply. I had mine blow once. I can't remember exactly how the P/S reacted but I believe it still did something like the LED flashing when the key was turned on.
If all that checks out, I am at a loss. Maybe someone else can help more that I have been able to. Either way, when you figure it out, please be sure to post the problem/cause repair here for everyones future reference.