When I start my MacBook Pro 2011 I get a grey screen only. Does anyone know what I can do?

Earlier today when using the same external monitor I've been using for several years my computer monitor became covered with thin black horizontal lInes. Then the computer monitor and the external monitor crossed one another. I couldn't access the Apple to restart so I had to shut down via power button. Now I can't get the computer to start. When I try to start it I get a grey screen only. Does anyone know what I can do?