Hi,
the "attachInterrupt(0, start, RISING);" was a try to get the external interrupt running because I couldn't make it with real "C" 
. And the ISR(EXT_INT0_vect) function is basically the double cover to the attachInterrupt...but both doesn't work... :~
The code in the ISR looks like it stops the timer by setting the control registers to 0.
I wanted to put the counter at least to zero. I again read the datasheet and should have put a zero value to the TCNT1 register and not to TCCR1* control register , right?
Perhaps you should move the code that starts the timer into start() and call it from your external interrupt instead of from setup().
I did not know that I started the timer...I thought it would be running anyhow. How can I start and stop it?