If your BitPixel has a black screen when initially powered on and when your ALU has been disconnected from BitPixel, then most likely BitPixel’s microSD card must be reset. 

Follow these steps to reset BitPixel’s microSD card:  

Step 1: Remove the microSD card from the back of the BitPixel board and insert into your PC or Mac using a microSD card to SD card adapter (not included with BitPixel purchase).

Step 2: Format the microSD card in your PC or Mac using this specific SD card formatting utility. 

Step 3: Unzip and then add the following 5 files to the root of the microSD card.

Your microSD card should then look like this. Note that the 5 files must be located in the root.

Step 4: Eject and insert the microSD card back into BitPixel and power cycle.