Why do i keep having this dream?

I had a dream a long time ago, years ago. I never forgot it. Now its back every few nights and just keeps coming. It's about me and a "haunted" house that's abandoned and old and the dream is always in black and white except for the grass, trees, lights, all normal, but the house is grey and black and i would go inside and its like if i don't get out i die. So i go in, and there's ghosts and demons, literally too many to count. But only one is good, and never shows til the end. There all these things to do and voices to hear telling me things. and theres a symbol for something. The main thing is that upstairs in an attic right before i get out of the house, i see my grandmother who has been dead for 2 years and 3 months. She never says anything, never looks at me. I jump out a window and when im outside i see more ghosts and spirits staring at me, then i wake up...