I suspect from your symptoms you have a problem with supply possibly by a bad earth and unfortunatley there are loads of them and you would need to study the current flow diagrams to try and narrow it down.
I would start by trying to code the battery if you have not done so already.
You can try holding the brake pedal depress to wake the car enough to get access to modules in VCDS.
Then go through each module with faults logged and clear each one individually because in my experience clear all dtc's does not work.
Then scan again to see what faults remain.
Then using VCDS and brake depressed if that worked open the measuring blocks for module 05 and see what the values are for block 1,1 Terminal status with the ignition on Terminal 15 should be on.
If it says on and there are no lights on dashboard remove fuse 1 form the end of the dashboard driver side, it should be a 5A fuse for the handbrake unit, test the terminals in the slot for the fuse and see if you have indeed power applied to that fuse when the ignition (Terminal 15) is meant to be on.
Report back what you find.
See this
thread for manuals and other info