When my computer goes to sleep I have to do SMC Reset?

Ok so when trying to wake my computer from sleep the other night my password login screen appeared then the screen went dark. I shut down the computer and powered it on again but the screen was still dark. I did about 3 SMC resets then the screen worked again. When i power down and boot up the computer every thing works fine, only when it goes to sleep does this problem happen any ideas of what might be causing it and how i could find out exactly what it is?