If your SD slot is on an ethernet shield, you will need to go thru a procedure to get both to work together. The below test code has a method to get both started. I've noticed that if I start the ethernet card the usual way, I have to power down the arduino before I can get the SD cared to work again.
//zoomkat 12/26/12
//SD server test code
//open serial monitor to see what the arduino receives
//address will look like http://192.168.1.102:84 when submited
//for use with W5100 based ethernet shields
#include <SD.h>
#include <SPI.h>
#include <Ethernet.h>
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //physical mac address
byte ip[] = { 192, 168, 1, 102 }; // ip in lan
byte gateway[] = { 192, 168, 1, 1 }; // internet access via router
byte subnet[] = { 255, 255, 255, 0 }; //subnet mask
EthernetServer server(84); //server port
String readString;
//////////////////////
void setup(){
Serial.begin(9600);
// disable w5100 while setting up SD
pinMode(10,OUTPUT);
digitalWrite(10,HIGH);
Serial.print("Starting SD..");
if(!SD.begin(4)) Serial.println("failed");
else Serial.println("ok");
Ethernet.begin(mac, ip, gateway, gateway, subnet);
digitalWrite(10,HIGH);
//delay(2000);
server.begin();
Serial.println("Ready");
}
void loop(){
// Create a client connection
EthernetClient client = server.available();
if (client) {
while (client.connected()) {
if (client.available()) {
char c = client.read();
//read char by char HTTP request
if (readString.length() < 100) {
//store characters to string
readString += c;
//Serial.print(c);
}
//if HTTP request has ended
if (c == '\n') {
///////////////
Serial.println(readString); //print to serial monitor for debuging
client.println("HTTP/1.1 200 OK"); //send new page
client.println("Content-Type: text/html");
//client.println("Content-Type: image/jpeg");
//client.println("Content-Type: image/gif");
//client.println("Content-Type: application/x-javascript");
//client.println("Content-Type: text");
client.println();
//File myFile = SD.open("boom.htm");
File myFile = SD.open("HYPNO.JPG");
//File myFile = SD.open("BLUEH_SL.GIF");
//File myFile = SD.open("SERVOSLD.HTM");
if (myFile) {
//Serial.println("test.txt:");
// read from the file until there's nothing else in it:
while (myFile.available()) {
client.write(myFile.read());
}
// close the file:
myFile.close();
}
delay(1);
//stopping client
client.stop();
readString="";
//}
}
}
}
}
}