Not uploading sketches onto board

So I have used Arduino for quite a while now, but recently I took a break for a while. I recently tried to upload some code to my arduino uno, and It uploaded correctly, but then, when I tried to upload a revision of the sketch, or even a totally new sketch, I get the error, avrdude: stk500_getsync(): not in sync: resp=0x00. So I switched over to my macbook pro version 10.5.8, and I uploaded a blank sketch, then a blinking led sketch, and then my code again. It all worked fine, but then when I tried to upload another sketch, I get, avrdude: stk500_recv(): programmer is not responding. Pressing the reset button and loading a blank sketch doesn’t work. My sketch that I loaded to my arduino is still on their, even when I press the reset button, or do anything really.
Here is my sketch,

#include <LiquidCrystal.h>
LiquidCrystal lcd(7, 8, 9, 10, 11, 12); // initialize the library with the numbers of the interface pins

#define TAG_LEN 12
char tag[12] = {'0', '1', '0', '0', '4', 'D', 'D', '1', 'D', '3'}; //tag 1
char tag2[12] = {'3', '6', '0', '0', '7', '8', '9', 'B', 'B', '5'}; //tag 2
char code[12];
int bytesread = 0;
//Connections to be made:
int ledPin = 13; // Connect LED to pin 13
int rfidPin = 2; // RFID enable pin connected to digital pin 2
//Connect SOUT Pin to pin 0, does not need to be defined because 0 is the default RX pin
int val=0;
void setup() {
lcd.begin(16, 2); // set up the LCD's number of rows and columns
lcd.print("Initializing...");
delay (1000);

Serial.begin(2400); // RFID reader SOUT pin connected to Serial RX pin at 2400bps 
pinMode(rfidPin,OUTPUT);   // Set digital pin 2 as OUTPUT to connect it to the RFID /ENABLE pin
pinMode(ledPin,OUTPUT); // Set ledPin to output

digitalWrite(rfidPin, LOW); // Activate the RFID reader
}

 void loop() {
digitalWrite(ledPin,LOW); //LED off
digitalWrite(rfidPin, LOW); // Activate the RFID reader
 lcd.clear(); //Clears LCD
 lcd.setCursor(0, 0);
 lcd.print("  Please Swipe");
 //lcd.setCursor(0, 1);
 //lcd.print("   Your Card");
  if(Serial.available() > 0) {	    // if data available from reader
    if((val = Serial.read()) == 10) {   // check for header
	bytesread = 0;
	while(bytesread<10) {		  // read 10 digit code
	  if( Serial.available() > 0) {
	    val = Serial.read();
	    if((val == 10)||(val == 13)) { // if header or stop bytes before the 10 digit reading
		break;			     // stop reading
	    }
	    code[bytesread] = val;	   // add the digit
	    bytesread++;			 // ready to read next digit
digitalWrite(rfidPin, HIGH); //Turns off RFID reader, THIS IS IMPORTANT so it doesn't double read the card
	  }
	}

	if(bytesread >= 10) {		  // if 10 digit read is complete
 
	 if(strcmp(code, tag) == 0) {
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print(" Access Granted");
 lcd.setCursor(0, 1);
 lcd.println(code);
 delay (1500);
 lcd.setCursor(0, 1);
 lcd.print("Jonnyblanch  ");
         digitalWrite(ledPin,HIGH);
	   Serial.print("Tag matches: ");
	   Serial.println(code);
           //digitalWrite(ledPin,HIGH);
           digitalWrite(rfidPin, HIGH);
            delay(2000);	     // wait for a second or two
           return;                   //Go to the top, skip the bottom
         }
         if(strcmp(code, tag2) == 0) {
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print(" Access Granted");
 lcd.setCursor(0, 1);
 lcd.println(code);
 delay (1500);
 lcd.setCursor(0, 1);
 lcd.print("Hector Lopez");
         digitalWrite(ledPin,HIGH);
	   Serial.print("Tag matches: ");
	   Serial.println(code);
           digitalWrite(ledPin,HIGH);
           digitalWrite(rfidPin, HIGH);
            delay(2000);	     // wait for a second
           return;
	   
	 }
	 else {
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print("Access Denied");
 lcd.setCursor(0, 1);
 lcd.println(code);
	   Serial.print(code);
	   Serial.println(" does not match");
           digitalWrite(rfidPin, HIGH);
           
	 }


	}
	bytesread = 0;
	     delay(2000);	     // wait for a second
        digitalWrite(ledPin,LOW);    
    }
  }
}

Alright, I figured it out, I had a wire going to digital pin 0, which I guess you can't have while uploading sketches.

I had a wire going to digital pin 0, which I guess you can't have while uploading sketches

This pin is involved with the upload using USB. You were preventing the upload by using this pin.