What I ought to say is just like there is no such thing as monster, there is no such monster as writer's block. In my experiences writing, just like texting, T.V., Play Station, Xbox etc., is a habit. And professional writers make that habit an addiction. Have a look at professional writers, most of them care least about their dresses and looks.
But the first thing that they care about is whether they have their notebooks, pen and pencils with them. Today, in spite of many technological advancements, most of the writers still prefer traditional Notebooks or Journals. That's the beauty of writing, it's natural.
When it comes to screenwriting, apart from the rough preparations, a computer or laptop is necessary for Formatting it. Because you can't let the rules and regulations come in the way of our creative process. Hence screenwriters prefer computer. Ultimately what counts is the Story and the way it is being told. Before writing a screenplay it is necessary to understand what it is? and what it's not? (Refer some books by Syd Field). A screenplay is a story told in pictures and you must keep it in mind.
You asked about inspiration, fine. What inspires me is music! I'll be waiting for the release of new albums so that I can get some inspiration by listening to them. Good musics trigger that creative energy for most of the people. But this isn't over yet. After you produce a concept and a rough story line within your mind, it's about travelling to different places, where you haven't been for a long time. This may help you in elaborating your concept into a story line.
Now comes the part where you divide your story line into beginning middle and end. And hence followed by characters. You must write some back stories and biographies about your Characters, spend some more time on this particular stage. Because most successful stories are character driven. Decide what genre you want to write.
For events that take place in the story, refer some newspapers if you think that your mind isn't producing satisfactory ideas. You can also turn on your TV, and keep changing the channels, and be surprised when an unexpected idea pops in outta nowhere!
If you are not able to write good dialogues, you can listen to a speech. If possible try listening to a speech on the related topic. And you can pay a visit to Cafe, listen to the people, find a person who looks similar to your character and listen to whatever he speaks. This is very helpful.
DREAM is an excellent source of idea for writers, particularly screenwriters. But make sure you make note of what dream you had immediately after you wake up. Some times crazy thoughts and quotes keep popping in outta nowhere. Note them before they are erased outta your memory. Also try writing about some of your own experiences.
This is what you can do. But this is what you don't do... Don't compare your material with other's, it's too misleading. When you tell your story to someone, if they respond with a strange expression don't think that they are not excited about your idea. They are excited about your idea. And sometimes they may smile at bad ideas to make others feel better

Don't try to be perfect, give your 110% and leave the rest to destiny. If you are writing for others then make sure you write what they want. If you are writing for your own movie, then feel free to express yourself. Don't burden yourself by trying to write all at once. Divide it into several sessions. Spend more time on re-writing rather than the first draft, according to my experience, first draft always stinks, it's never great. It's just like a JIGSAW puzzle. Rewriting is more like solving a puzzle. Remember great stories have great conflict, so during ACT 2 try getting into the feet of Hitler and trouble your Character, be merciless. During ACT 3 get into the feet of Jesus and give your Character a perfect, happy ending.
And make sure that you pitch your material effectively. This is by far the most important stage of screenplay marketing. Get into the feet of Bill Gates during this stage. Stay in contact with the person to whom you want to sell the Script.
All the best and happy Screenwriting
