SD card not working - Arduino Mega 2560 + Ethernet shield

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Hello,

I'm new in this forum. I'm hading a hard time getting the SD card to work.

I have Arduino Mega 2560 and a standard Ethernet+SD Shield.

My SD card is a Sandisk SDHC 8GB, formatted as FAT16 with one primary 2GB partition. I used windows DISKPART to do that.

I have also tried this same SD card formated in factory defaults (FAT32 + 8GB partition). Also tried a different SD card as well.

My shield looks like this:

http://cloud3.lbox.me/images/384x384/201206/eletronica-diy-arduino-ethernet-shield-w5100_qnfgjz1339666028684.jpg

As I have two identical shields, I tried to replace the shield, and the same error ocurred.

My code:

#include <SD.h>
#include <SPI.h>
#include <LiquidCrystal.h>

LiquidCrystal lcd(8,9,4,5,6,7); 

void setup() {
 pinMode(10, OUTPUT);
  digitalWrite(10, HIGH);
  
    if (!SD.begin(4)) {
     lcd.println("Error reading SD!");
       }
    else{
      lcd.print("SD OK!");
   }

}

void loop() {
  // put your main code here, to run repeatedly:

}

It always fails in SD.begin, and shows the message "Error reading SD!"

I have read dozens of forum posts, tried many things, with no success. :o

Any ideas?

Thanks!!