Problem with MAX7219

Hello all

I am trying to display some digits on a 3 digit 7 segment display but for some reason i have some problems with it

below you will find the fritz how everything is connected

The 7 segment is Common Cathode

I use the example sketch LCD Demo 7 segment

//We always have to include the library
#include "LedControl.h"

/*
 Now we need a LedControl to work with.
 ***** These pin numbers will probably not work with your hardware *****
 pin 12 is connected to the DataIn 
 pin 11 is connected to the CLK 
 pin 10 is connected to LOAD 
 We have only a single MAX72XX.
 */
LedControl lc=LedControl(12,11,10,1);

/* we always wait a bit between updates of the display */
unsigned long delaytime=250;

void setup() {
  /*
   The MAX72XX is in power-saving mode on startup,
   we have to do a wakeup call
   */
  lc.shutdown(0,false);
  /* Set the brightness to a medium values */
  lc.setIntensity(0,8);
  /* and clear the display */
  lc.clearDisplay(0);
}


/*
 This method will display the characters for the
 word "Arduino" one after the other on digit 0. 
 */
void writeArduinoOn7Segment() {
  lc.setChar(0,0,'a',false);
  delay(delaytime);
  lc.setRow(0,0,0x05);
  delay(delaytime);
  lc.setChar(0,0,'d',false);
  delay(delaytime);
  lc.setRow(0,0,0x1c);
  delay(delaytime);
  lc.setRow(0,0,B00010000);
  delay(delaytime);
  lc.setRow(0,0,0x15);
  delay(delaytime);
  lc.setRow(0,0,0x1D);
  delay(delaytime);
  lc.clearDisplay(0);
  delay(delaytime);
} 

/*
  This method will scroll all the hexa-decimal
 numbers and letters on the display. You will need at least
 four 7-Segment digits. otherwise it won't really look that good.
 */
void scrollDigits() {
  for(int i=0;i<13;i++) {
    lc.setDigit(0,3,i,false);
    lc.setDigit(0,2,i+1,false);
    lc.setDigit(0,1,i+2,false);
    lc.setDigit(0,0,i+3,false);
    delay(delaytime);
  }
  lc.clearDisplay(0);
  delay(delaytime);
}

void loop() { 
  writeArduinoOn7Segment();
  scrollDigits();
}

my problems are 2

1 if i read the schematic of MAX7219 correctly i should connect the arduino gnd with PIN 4 & 9 if i do that the 7 segment is flashing and doesn't show anything.

2 If i leave the gnd unconnected then the 3 digit 7segment shows the half of the things that should be shown and then it switches off.

Any ideas why ?

if i read the schematic of MAX7219 correctly i should connect the arduino gnd with PIN 4 & 9

Yes that is correct.

if i do that the 7 segment is flashing and doesn't show anything.

So all that means is you have something else wrong.

If i leave the gnd unconnected then .......

That is silly, it dosn't tell you anything. It is like saying, "if I screw this up then something happens", so what? It is screwed up.

below you will find the fritz how everything is connected

No, by definition it is a Fritzing physical layout diagram and is useless to see what your circuit is. Draw a schematic by hand and label all the connections to the MAX7219. You also need decoupling capacitors on this chip, like you do with every chip. See:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html