MacBook Pro won't awake from sleep.

Hi, I have a Mid 2010 15in MacBook Pro running OS 10.7 Lion. I have had this problem for about 2 months now. Basically I will be using my MacBook Pro, then when I'm done using it I will shut the lid. When I come back to use it again I open the lid and there's just a black screen. Sometimes the Screen is black sometimes its gray. The backlit keyboard is on but the screen is either Black or gray. When I shut the MacBook Pro lid again the Indicated light comes on. Then when I open the lid the Indicator light goes off. The only way to fix this is to hold down the power button. Please Help!