Professionals would say "writer's block" doesn't exist. They have contracts with publishers and deadlines to meet and they have to get on with the "day job" same as everyone else, but...
"It's just that it's so hard..." (Prince Arthur character in Shrek 3). And it is. Really. Really hard. And sometimes you just want to give up, and your enthusiasm and ideas evaporate, and that's when the ole block of concrete falls out of the sky and drops on your head.
The thing is, writing is a subjective and emotional activity, as are all creative arts, so a good dose of inspiration is vital. However, in the real world, successful writers will tell you the inspiration is only the 1% and the remaining heavy digging, I'm afraid, is 99% (Thomas Edison, if you want to check it out).
Having said that, the first thing is not to beat yourself up. Writers are notoriously over-sensitive souls. They have to be, to tackle those life and death issues that inspire them in the first place.
Top Tips to beat the writer's block:
Make a regular writing time and always sit at the blank sheet of paper for at least half an hour. Learn not to be scared of it, and write anything - notes, a character description, keywords for an outline, post some tweets, compose a kick-ass Facebook post. Always do this, every day. Serious writers write something every day.
Take a break. Get up from the desk. Walk the dog. Go for a swim. Have a coffee, scoff some carbs, give yourself a sugar rush. Do deep breathing. Do the vacuuming. Give your brain a treat. Turn the music up. Anything.
Recognise that a piece of written work is an organic, evolved product of your brain. Sometimes you can't rush it and your subconscious is working on an issue that you can't solve immediately. Read Stephen King's On Writing.
Work on something else. This is often the most effective solution.
Don't beat yourself up. To produce top quality written work is difficult, very difficult (otherwise everybody would be doing it. lol) It takes talent, creativity, skill learned over decades, focus and faith in yourself.
Get some feedback. I have a small group of writer friends (serious writers) and from time to time we critique each other's work. It really helps.
Join a class or writing group. You'd be amazed how much collective inspiration there is.
So, as I said, don't beat yourself up. Be patient with yourself, but at the same time develop the discipline of a daily habit, interact with other writers, read writers who inspire you, and keep going. Don't worry about the writer's block, but look for ways round it.