Hello jasona99, Just to let you know I also used the "Lapdock 100" For Droid Razr and I was having the exact same problem as you...
plug HDMI, screen turns on, 5 sec later, screen shuts down but pi is powered, then dies.
what was happening to me was that it seems that with all my tests I broke my USB ports

. I tested with a different RPi and it's working now.
How to check if this is your problem:
edit your config.txt and add these lines to force hdmi output:
Code: Select all
hdmi_safe=0
hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=47
hdmi_drive=2
hdmi_boost=4
1. plug the RPi to a power source,
2. immediately plug the HDMI cable from RPi to the lapdock - may have to wait, if done continuously it does not work, sometimes I had to wait for about 15 mins for it to respond.
3. immediately plug the USB port from lapdock to PC (yes, PC, not RPi).
I could see the image of the RPi on the lapdock and control my PC with lapdock's mouse/keyboard, the screen did not shut down since the USB was connected to the PC.
So in my case I had a faulty USB and USB is necesary for the lapdock to keep the screen active.