HIGH and LOW reversed
With the given schematic both your logic for segments and digits should be active high, so it looks like you made a mistake. Especially because you say it doesn't work anymore when you connect ground. Check that you have the right transistor and that it's connected correctly: Emitter should go to ground, collector to the display's common cathode. (Check that your displays are common cathode!)

It's not a good idea to define some version of high as low, that's only confusing. Instead name the signals:



#define DISPLAY_SEGMENT_ON HIGH
#define DISPLAY_DIGIT_ON HIGH


The image can be found at several places on the Internet, so I guess you didn't draw it. This is a common cathode display, and the transistors are NPN types. If your displays are common anode then the whole thing flips upside-down: The Ground rail becomes Vcc, and the NPN transistors should be PNP types. Then you will indeed have inverted logic, and you should define:

#define DISPLAY_SEGMENT_ON LOW
#define DISPLAY_DIGIT_ON LOW