I'd say distraction is my problem. The internet, people and family coming over and talking. Things that grab my attention. They can also be source of ideas though.

What works is lowering expectations. Instead of thinking I have to write a 4,000-word chapter, I imagine working on a 400-word piece. Once I write a scene or a bit of dialog, the ideas start to flow and it's hard to stop them. The first page of the blank document is the obstacle to overcome.