My ASUS R500A will turn on but screen is black.

The HDD and wifi light flash on and off rapidly. Intially I used to be able to shut it down and turn it on again and everything would come on including the screen. Now the screen will not come on and at times the HDD light and wifi light also will not turn on. WHen that occurs the fan doesn't run either. I have tried to reseat the ram and have also replaced the cmos battery. still not working. Any thoughts on what I should do next?