why isnt LED lighting?

I have exactly the same commands as in the blink tutorial, which works fine. But in this program the LED doesnt blink. It makes a tiny blip each time it goes thru the loop, but it does that without any digitalWrite commands. Why doesnt it turn on?

//******** include statements, constants  ***********

// **** for datalog
#include <SPI.h>  
#include <SD.h>  
const int chipSelect = 10;

// **** for RTC     // Date and time functions using a DS1307 RTC connected via I2C and Wire lib                  
#include <Wire.h>
#include "RTClib.h"
#if defined(ARDUINO_ARCH_SAMD)  // for Zero, output on USB Serial console, remove line below if using programming port to program the Zero!                  
   #define Serial SerialUSB
#endif
RTC_PCF8523 rtc;

// **************  initialize date, analog port, SD card   *******************

void setup () {     //*** begin setup 

#ifndef ESP8266
    while (!Serial); // for Leonardo/Micro/Zero
#endif

   Serial.begin(9600);
   if (! rtc.begin()) {Serial.println("Couldn't find RTC");  while (1);  }   // RTC
   if (! rtc.initialized()) {Serial.println("RTC is NOT running!"); }

   Serial.print("Initializing SD card...");  // see if the card is present and can be initialized:
   if (!SD.begin(chipSelect)) {
   Serial.println("Card failed, or not present");
                              // don't do anything more:
    while (1);
  }
  Serial.println("card initialized.");
  pinMode(LED_BUILTIN, OUTPUT);
  
}                    //*** end setup


// ******************  Main loop  **********************

void loop () {
/*digitalWrite(LED_BUILTIN, HIGH);  
delay(3000);
digitalWrite(LED_BUILTIN, LOW);  
delay(1000);
*/  
  DateTime now = rtc.now();
  String dataString = "";   // make a string for assembling the data to log:
  dataString += String(now.year());  // insert date & time in string
  dataString += "/";
  dataString += String(now.month());
  dataString += "/";
  dataString += String(now.day());
  dataString += " ";
  dataString += String(now.hour());
  dataString += ":";
  dataString += String(now.minute());
  dataString += ":";
  dataString += String(now.second());
  dataString += " ";
  
  for (int analogPin = 0; analogPin < 3; analogPin++) {      // read analog inputs 1,2,3 and append to the string:
    int sensor = analogRead(analogPin);
    dataString += String(sensor*4.8*4*1);  // analog input has values between 0 and 1024, 0-5V, the bridge divides voltage by 4, hence multiply result by 4.8*4, 
    if (analogPin < 2) { 
      dataString += ",";
    }
  }

  File dataFile = SD.open("solog4.txt", FILE_WRITE);   // open the file. note that only one file can be open at a time so you have to close this one before opening another.

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
    delay(2000);  // to take sample every 10 mins - set to 600000
    Serial.println(dataString);  // print to the serial port too:
  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error opening datalog.txt");
  }

}   //   ************** end main loop

#include <SPI.h>  Are we talking about the LED on pin 13?

This is not a trick question! Sorry I forgot to uncomment the digitalWrite commands. (and the Forum is making me wait 5 mins to post) Here is the correct code. Why doesnt the LED turn on?

//******** include statements, constants  ***********

// **** for datalog
#include <SPI.h>  
#include <SD.h>  
const int chipSelect = 10;

// **** for RTC     // Date and time functions using a DS1307 RTC connected via I2C and Wire lib                  
#include <Wire.h>
#include "RTClib.h"
#if defined(ARDUINO_ARCH_SAMD)  // for Zero, output on USB Serial console, remove line below if using programming port to program the Zero!                  
   #define Serial SerialUSB
#endif
RTC_PCF8523 rtc;

// **************  initialize date, analog port, SD card   *******************

void setup () {     //*** begin setup 

#ifndef ESP8266
    while (!Serial); // for Leonardo/Micro/Zero
#endif

   Serial.begin(9600);
   if (! rtc.begin()) {Serial.println("Couldn't find RTC");  while (1);  }   // RTC
   if (! rtc.initialized()) {Serial.println("RTC is NOT running!"); }

   Serial.print("Initializing SD card...");  // see if the card is present and can be initialized:
   if (!SD.begin(chipSelect)) {
   Serial.println("Card failed, or not present");
                              // don't do anything more:
    while (1);
  }
  Serial.println("card initialized.");
  pinMode(LED_BUILTIN, OUTPUT);
  
}                    //*** end setup


// ******************  Main loop  **********************

void loop () {
digitalWrite(LED_BUILTIN, HIGH);  
delay(3000);
digitalWrite(LED_BUILTIN, LOW);  
delay(1000);
 
  DateTime now = rtc.now();
  String dataString = "";   // make a string for assembling the data to log:
  dataString += String(now.year());  // insert date & time in string
  dataString += "/";
  dataString += String(now.month());
  dataString += "/";
  dataString += String(now.day());
  dataString += " ";
  dataString += String(now.hour());
  dataString += ":";
  dataString += String(now.minute());
  dataString += ":";
  dataString += String(now.second());
  dataString += " ";
  
  for (int analogPin = 0; analogPin < 3; analogPin++) {      // read analog inputs 1,2,3 and append to the string:
    int sensor = analogRead(analogPin);
    dataString += String(sensor*4.8*4*1);  // analog input has values between 0 and 1024, 0-5V, the bridge divides voltage by 4, hence multiply result by 4.8*4, 
    if (analogPin < 2) { 
      dataString += ",";
    }
  }

  File dataFile = SD.open("solog4.txt", FILE_WRITE);   // open the file. note that only one file can be open at a time so you have to close this one before opening another.

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
    delay(2000);  // to take sample every 10 mins - set to 600000
    Serial.println(dataString);  // print to the serial port too:
  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("error opening datalog.txt");
  }

}   //   ************** end main loop

You're using SPI. What SPI function does pin 13 serve?

Yes. I assume LED_BUILTIN is the one on 13.

AWOL - are you suggesting that pin 13 is being used by something else, which is why I cant light it? I dont know what SPI function pin 13 serves. (I’m still a Noob) Is there perhaps another LED I can use?

Help is at hand

It appears the SPI is using pin 13. Is this why I cant light it?
I believe the include SPI is for data logging. Can I still log if I delete the include SPI statement?
Can I override it for the LED without hurting anything?

What I wanted was something to tell me the program is working (logging) while running off a
battery (i.e. blink the LED when logging to let me know the code is not stuck somewhere). Do you have any suggestions? Is there another LED onboard that I can use?

You could add another LED. Don't forget to use a current-limiting resistor, and to choose a pin that isn't already in use.

Roger that. Thanks for your help.