AVR Atmega8 ADC input causes Crash - avr

Question

i am trying to Read an Voltage Level via a ADC0 of my ATmega8, because of querying a 1 Pin 4x4 Matrix Keypad. The Problem is everytime I apply a Voltage to the ADC higher than GND the Atmega is stopping to do his work. The PWM outputs are still working, but communication via i2c is impossible and the LCD is clear.
My wiring is simple, AREF & AVCC are set to 5V, GND is set to GND and PC0 is my Input. Is there anything I fail to Notice? Thank You for your help.
Here is my Code:
void Initialisierung(void)
{
char text [2];
lcd_init();
cli();
//### TWI
init_twi_slave(SLAVE_ADRESSE); //TWI als Slave mit Adresse slaveadr starten
sei();
lcd_setcursor( 0, 1 );
lcd_string(">Booting...");
lcd_setcursor( 0, 2 );
itoa (SLAVE_ADRESSE,text,16);
lcd_string("I2C Adress=0x");
lcd_string(text);
for (int Index=0; Index<85; ++Index) {
rxbuffer[Index] = 0x20;
}
rxbuffer[81]=0xFF;
rxbuffer[82]=0xFF;
rxbuffer[83]=0xFF;
rxbuffer[84]=0xFF;
}
//update LCD
void lcd_update(void){
for (int o=1;o<=4; o++)
for (int i=1; i<=20; i++){
lcd_setcursor( i-1, o );
lcd_data(rxbuffer[i+((o-1)*20)]);
}
}
An here is the main function:
int main(void)
{
DDRC &= ~(1 << PC0);
PORTC &= ~(1 << PC0);
Initialisierung();
DDRB = (1 << DDB1) | (1 << DDB2);
OCR1A = eeprom_read_word(&brightness); // PWM einstellen,
OCR1B = eeprom_read_word(&contrast);
ICR1 = 1000; // TOP-wert
TCCR1A = (1<<COM1A1) | (1<<COM1B1) | (1<<WGM11); // 2-Kanal "non-inverting"
TCCR1B = (1<<WGM13)|(1<<WGM12) | (1<<CS11);
//Initialize ADC
ADCSRA = (1<<ADEN) | (1<<ADPS2) | (1<<ADPS0);
ADMUX=0x00;
unsigned int adc_value=0; // Variable to hold ADC result
char text[2];
while(1)
{
ADCSRA |= (1<<ADSC); // Start conversion
while (ADCSRA & (1<<ADSC)); // wait for conversion to complete
adc_value = ADCW; //Store ADC value
itoa (adc_value,text,16);
lcd_setcursor( 0,4 );
lcd_string(text);
for (int Index=0; Index<85; ++Index) {
txbuffer[Index] = rxbuffer[Index];
}
uint16_t brightness_i2c=0;
uint16_t contrast_i2c=0;
brightness_i2c=(rxbuffer[81]<<8)|(rxbuffer[82]);
contrast_i2c=(rxbuffer[83]<<8)|(rxbuffer[84]);
if (rxbuffer[0]==1){
lcd_update();
rxbuffer[0]=4;
}else if(brightness_i2c!=eeprom_read_word(&brightness) && brightness_i2c!=0xFFFF){
eeprom_write_word(&brightness,brightness_i2c);
OCR1A = eeprom_read_word(&brightness);
}else if (contrast_i2c!=eeprom_read_word(&contrast) && contrast_i2c!=0xFFFF){
eeprom_write_word(&contrast,contrast_i2c);
OCR1B = eeprom_read_word(&contrast);
}else{
for (uint8_t i=0; i<50; i++) _delay_ms(10);
lcd_setcursor( 19, 4 );
lcd_data(0xFF);
for (uint8_t i=0; i<50; i++) _delay_ms(10);
lcd_setcursor( 19, 4 );
lcd_data(0x20);
}
}
}

Answer 1

I finally got it:
I setup the ADC with interrupts but not freerunning:
ADCSRA =(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADIE)| (1<<ADPS0);
And call the ADC everytime at the end of my While loop:
ADCSRA |= (1<<ADSC);
Here is the Code for the ISR:
ISR(ADC_vect)
{
char text[5];
itoa (ADC,text,16);
lcd_setcursor( 0,4 );
lcd_string(text);
}
Thanks for your time ;)