Need Help with Datalogger, wont write to SD

Other Hardware Storage
1

I have built a simple temperature sensor with a TMP36 connected to Analog 0. and a Ready LED (Red) on Pin 2 and a Start LED (Green) On pin 8. At the beginning of the program, it writes a simple text string to the SD in a file called Test.txt. In the loop, it is supposed to write the sample number and the temperature to the SD in the same file (for now) but it wont do that, it stops after it writes the test to the SD and then it stays there. It is getting really frustrating becuase i know the SD card is formatted correctly and its all hooked up right. Any suggestions? Thanks.

Code:

#include <toneAC.h>
#include <SPI.h>
#include <SD.h>
int readyLED = 4;
int startLED = 8;
int buzzer = 7;
int tempSensor = A0;
int readyButton = 5;
int sampleNo = 0;
int button_mode = 1;
File myFile;
void setup() {
  // put your setup code here, to run once:
 pinMode(readyLED, OUTPUT);
  pinMode(startLED, OUTPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(tempSensor, INPUT);
  pinMode(readyButton, INPUT);
  digitalWrite(readyLED, HIGH);
  digitalWrite(startLED, LOW);
  Serial.begin(9600);
  while (!Serial){}
    Serial.println("Initializing SD card...");
  if(!SD.begin(4)){
      Serial.println("Failed!");
      return;
    }
  Serial.println("Success!");
    myFile = SD.open("test.txt", FILE_WRITE);
     if (myFile) {
    Serial.println("Writing to test.txt...");
    myFile.println("testing 1, 2, 3.");
    delay(500);
    myFile.close();
    Serial.println("done.");
      } else {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
  }
  delay(1000);
  } 


void loop() {
  // put your main code here, to run repeatedly:
   digitalWrite(startLED, LOW);
    digitalWrite(readyLED, LOW);
    delay(650);
    digitalWrite(startLED, HIGH);
    digitalWrite(readyLED, LOW);
    delay(650);
    int reading = analogRead(tempSensor);  
    float voltage = reading * 5.0;
    voltage /= 1024.0; 
    float temperatureC = (voltage - 0.5) * 100;
    float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
    Serial.print("Sample No. ");
    sampleNo = sampleNo + 1;
    Serial.print(sampleNo);
    Serial.print(" Temperature: ");
    Serial.print(temperatureF);
    Serial.println(" F");
    myFile = SD.open("test.txt");
    if(myFile){
      Serial.println("Test.txt");
      }
      while(myFile.available()){
        myFile.print("Sample No. ");
        myFile.print(sampleNo);
        myFile.print(" Temperature: ");
        myFile.print(temperatureF);
        myFile.println(" F");       
      }
      myFile.close();
}

the Serial output at the time of freezing

Initializing SD card...
Success!
Writing to test.txt...
done.
Sample No. 1 Temperature: 72.08 F
Test.txt

The Files on the SD after running:
TEST.txt

And on that file is:
testing 1, 2, 3.

2

read or write? => myFile = SD.open("test.txt");

3

I added FILE_WRITE to the loop where the file is opened but the files still dont show up

4

FILE_WRITE: open the file for reading and writing, starting at the end of the file.

while(myFile.available())//Check if there are any bytes available for reading from the file.

You open at the end of the file, there are no bytes out there to read, so it reports 0 and the file does not get written. Yo do not need the available test as you know the file is there to be written with the if(myFile) condition.