Help using Interrupt on Timer1 on Uno

Using Arduino Programming Questions
1

I'm learning how to use interrupts and created a small code to figure out how to work them. The code is supposed to print a counter to the serial monitor at a specific interval and flash the LED. The code uploads to the Uno but nothing appears on the serial monitor and the LEd doesn't flash. I have no idea what could be going wrong with it. Any ideas?

I have tried it on two different boards, so it isn't a bad Uno or anything.

volatile int counter = 0;

void timer1_init(){
  noInterrupts(); // disable interrupt
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 0; // initialize the counter from 0
  OCR1A = 7811; // sets the counter compare value. Using timer1, Prescaler= 1024, Interrupt frequency = 2 Hz, Compare value=[16e6/2/1024]-1= 7811
  TCCR1B |= (1<<WGM12); // enable the CTC mode
  TCCR1B |= (1<<CS12)|(1<<CS10); //sets the control scale bits for the timer
  TIMSK1 |= (1<<OCIE1A); //enable the interrupt
  interrupts(); //allows interrupts
  }
 
void setup() {
  pinMode(13, OUTPUT);
  digitalWrite(13, LOW);
  Serial.begin(115200);
  timer1_init();
  }

ISR(Timer1_COMPA_vect)  {
  counter += 1;
  Serial.print(counter);
  digitalWrite(13, HIGH);
  delay(100);
  digitalWrite(13, LOW);
  }

void loop(){
  }

Thank you.

2

Don't do serial I/O in interrupt context.

Don't do delay in interrupt context.

I'm pretty sure this is covered in the reference.