The printrbot USB is acting up, you can only control it via the LCD screen.
To use, slice files (with cura) and put them on the microSD card. The microsd is a bit hard to access since it is under the bed.
Firmware is based on Printrbot's marlin firmware  with the Z endstop changed (needs to be non inverted). Firmware should be located on the Slicing computer. To upload firmware, you need to use a separate arduino as ISP.
Command to download firmware:
C:\Arduino1.5.6\hardware\tools\avr\bin>avrdude -c avrisp -P COM14 -p at90usb1286 -U flash:w:Marlin.cpp.hex:i -C ..\etc\avrdude.conf -b 19200
The filament spool holder doesn't do well if the filament is below the extruder. I recommend putting the filament spool on top of the Dimension printer.