Arduino Ethernet Shield with SD Card does not le the html file

Hello, I have a problem, my Ethernet Shield does not start the SD Card, it gives the following error: "ERROR - SD card initialization failed!". Can someone help me?

PS: I'm using Arduino Mega

Code:

#include <SPI.h>
#include <Ethernet.h>
#include <SD.h>
int chipSelect = 4;
// MAC address from Ethernet shield sticker under board
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 0, 101); // IP address, may need to change depending on network
EthernetServer server(80);  // create a server at port 80

SDFile webFile;

void setup()
{
pinMode(53, OUTPUT);
Ethernet.begin(mac, ip);  // initialize Ethernet device
server.begin();           // start to listen for clients
Serial.begin(9600);       // for debugging

// initialize SD card
Serial.println("Initializing SD card...");
if (!SD.begin(4)) {
    Serial.println("ERROR - SD card initialization failed!");
    return;    // init failed
}
Serial.println("SUCCESS - SD card initialized.");
// check for index.htm file
if (!SD.exists("index.htm")) {
    Serial.println("ERROR - Can't find index.htm file!");
    return;  // can't find index file
}
Serial.println("SUCCESS - Found index.htm file.");
}

void loop()
{
EthernetClient client = server.available();  // try to get client

if (client) {  // got client?
    boolean currentLineIsBlank = true;
    while (client.connected()) {
        if (client.available()) {   // client data available to read
            char c = client.read(); // read 1 byte (character) from client
            // last line of client request is blank and ends with \n
            // respond to client only after last line received
            if (c == '\n' && currentLineIsBlank) {
                // send a standard http response header
                client.println("HTTP/1.1 200 OK");
                client.println("Content-Type: text/html");
                client.println("Connection: close");
                client.println();
                // send web page
                webFile = SD.open("index.htm");        // open web page file
                if (webFile) {
                    while(webFile.available()) {
                        client.write(webFile.read()); // send web page to client
                    }
                    webFile.close();
                }
                break;
            }
            // every line of text received from the client ends with \r\n
            if (c == '\n') {
                // last character on line of received text
                // starting new line with next character read
                currentLineIsBlank = true;
            } 
            else if (c != '\r') {
                // a text character was received from client
                currentLineIsBlank = false;
            }
        } // end if (client.available())
    } // end while (client.connected())
    delay(1);      // give the web browser time to receive the data
    client.stop(); // close the connection
} // end if (client)
}