Arduino Uno cannot read from SD card

Hello,
I'm trying to diagnose why is the SD card reader not working with Arduino Uno. I've connected the reader to the board the same way I did with 5-6 Uno boards (which are working) but the SimpleSDAudio doesn't seem to work, the sound just doesn't play.
Here is the code to check if the Arduino Uno can find the file (messy but it is):

#include <SPI.h>
#include <SD.h>
#include <sd_l0.h>
#include <sd_l1.h>
#include <sd_l2.h>
#include <SimpleSDAudio.h>
#include <SimpleSDAudioDefs.h>

int motion_1 = 2;
int light_1 = 13;
void setup(){
  pinMode (motion_1,INPUT);
  pinMode (light_1, OUTPUT);
  //pinMode (10, OUTPUT);
}

void loop (){
  if (SD.exists("1.AFS")){
    digitalWrite (light_1, HIGH);
    delay(2000);
    digitalWrite (light_1, LOW);
    delay(2000);
  }
  else if (!SD.exists("1.AFS")){
    digitalWrite (light_1, HIGH);
    delay(500);
    digitalWrite (light_1, LOW);
    delay(500);
  }
}

Of course the LED diode changes its state every half a second which means that this file cannot be found. My SD card is fully functional, it works on my computer and contains the 1.AFS file.
Here's how I connected those two elements:
(SD card reader) (Arduino)
CS - D4
MOSI - D11
3.3V - 3.3V
SCK - D13
MISO - D12
GND - GND

How can I diagnose the problem? I'm starting to think that either my Arduino or SD card reader is broken.

Also here's the code for playing the sound - "void setup" is the same as in the previous code snip:

void loop (){
  SdPlay.init(SSDA_MODE_FULLRATE | SSDA_MODE_STEREO | SSDA_MODE_AUTOWORKER);
  SdPlay.setFile("1.AFS");
  SdPlay.play();
  delay(500);
}

Just out of curiosity, is the file in a folder?

GreggG:
Just out of curiosity, is the file in a folder?

No, the file is in the root directory. There are no other files and folders as well, only "1.AFS".