MKR GSM 1400 program causes USB error

When I add an interrupt to my code, the MKR is no longer recognized by my development IDE.
I can't even seem to reinstall the bootloader.

Any ideas? - I have 4 MKR now that I can't use.

Here is a code snippet

// the setup function runs once when you press reset or power the board
#define RED_LED 9
#define GREEN_LED 8
#define PB 6

volatile bool m_PB_Down = false;
volatile bool m_B_Down = false;

void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(RED_LED, OUTPUT);
pinMode(GREEN_LED, OUTPUT);
pinMode(PB,INPUT);

// TURN ON GREEN LED
//Green_Led_Status(HIGH);
attachInterrupt(digitalPinToInterrupt(PB),PB_ISR, LOW);

}

void loop() {

if (m_PB_Down) {
Red_Led_Status(HIGH);
Green_Led_Status(LOW);
m_PB_Down=false;
}
}

void PB_ISR(){
m_PB_Down = true;
}

(deleted)

spycatcher2k:
Here is a snippet of my answer :

Hi - all you need to do is . . . . .

:smiley:

I love how newbies who don't know anything presume to spoon feed us what they believe is "relevant" to their problem.

.

Double click the RESET button to force the board into bootload mode then upload the BLINK sketch. If this works, the board and bootloader are OK.