Speaking from my own perspective, the type of writer's block I am addressing is not trauma bases, where there is a death in the family, but rather the common persistent ones, which sprout up at the most inconvenient times. But ask yourself:
"Is this type of writer's block a hurdle in the road, Or perhaps what you have currently stored within your subconscious, the unformed, is a better idea than what you, the conscious, is working with?"
A concept which came to me over time. Once I accepted this reality I no longer fought my blocks. I listen to music, stream the web, watch netflix, my dvds; whatever to get my mid off the 'here and now.' Once my body relaxes the hidden thoughts flow through me. I may from different periods, while engaging these deliberate distractions, pause to jot down notes in the document; as a way of guiding my process.
This exercises continues till nothing from the ether comes forth. After such, I organize the jumble lines to a workable paragraph, or passage. Polish it to a satisfactory result, and move forward.
How long does this process last? The results vary, but at least you'll be on a progressive track. Within time the gap between then and now is less.