Try to make a hardware reset (unplug the power cable then hold the power button for 10 sec then plugging the power cable back in) if that did not help. you must connect external monitor to see what is going on.
if that dose not help then it could be a hardware problem, if you are getting contentious flashing light on the front panel this could be the reason. in that case I would suggest that you take the hard drive a part and put it in external HDD and get your files.