Problem with code for IR remote controlled robot
Try replacing you loop function with this one.  It won't fix it.

void loop() 
{
    if (irrecv.decode(&amp;results))
    { 
        Serial.println(results.value, HEX);

        switch (results.value)
        {
        case Straight:
            moveForward();
            break;
        case Right:
            turnRight();
            break;
        case Left:
            turnLeft();
            break;
        case Back:
            moveBackward();
            break;
        default:
            Stop();
        }
        irrecv.resume();
    }
    else
    {
        Serial.println ("Nothing received");    // This message will annoy you so comment it out as soon as you are happy with what is happening.
    delay(100);
}


The switch statement is just a neater way of doing your ifs.  The Nothing received message will show you if decode is ever returning.  If it is returning you need to work out why it is returning false, by looking in the library code.  If it isn't returning then you need to look in the library code and see why.  If it is returning, but not giving you an expected value, you need to look in the library code and see why.

Sorry but from what you describe it seems to be an issue with the library or your use of it, could be anything, but when you can get some more info post it back here.