MacBook Air Not Turning On

Hi, my Macbook Air 11" mid-2011 suddenly won't start up. The charger is showing the orange light. I have reset the SMC, during which the charger went to green and then to orange. The laptop is hot from charging, and the fans go when I press the power button, and turn off when I hold it down again. The key backlights are not on, and the caps lock light does not go on. I have connected it to an external display, but it shows no signal. I have not damaged it or spilt anything on it.

What do you think has happened and what should I do?