Attiny not working after ADC conversion
I do not have any Attiny85 but I used your code and I write it to Attiny13. 

The code I used:

#include &lt;avr/io.h&gt;

uint8_t adc_result = 0;

int main( void ) {

    DDRB |= ( 1 &lt;&lt; DDB0 ); //set PB0 to output
    ADMUX  |= ( 1 &lt;&lt; ADLAR ) | ( 1 &lt;&lt; MUX1 ); //set ADC 2 (PB4), left adjust result
    ADCSRA |= ( 1 &lt;&lt; ADEN ); //enable ADC
    ADCSRA |= ( 1 &lt;&lt; ADPS1 ) | ( 1 &lt;&lt; ADPS2 ); //prescaler 64

    while ( 1 ) {

        ADCSRA |= ( 1 &lt;&lt; ADSC ); //start conversion

        while ( ADCSRA &amp; ( 1 &lt;&lt; ADSC ) );//wait for conversion to end

        adc_result = ADCH; //adc results (should be 0)

        PORTB ^= ( 1 &lt;&lt; PB0 ); //Toggle LED at PB0 

    }

    return( 0 );
}   


As you can see I slightly modified the code because My C compilers do not recognize _BV macro so, I replace it with (1 &lt;&lt; x) instead. 
And I also Toggle the led (PB0). 

And the signal at PB0 pin looks like this: 

         

Notice the signal frequency is around 5.2MHz.  

So it's is very interesting why this code don't work at attiny85.