If you can't write anything in your current project the best cure is to just open a new word file and type in it. Even if all you're typing is 'I can't write, I can't write, bullshit bullshit bullshit' just try to type some whole sentances out. Once the bad writing has left your system then you can turn back to your original project.
Lot's of people have said to get inspired. It's true, writing is a lot easier to do when you're inspired to do it. But you don't need inspiration to get any decent work done. Some of the best stuff I've written has come out during those times when I've forced myself to write when I didn't want to.
Try setting yourself a daily word limit that you can achieve - like 1,000 words, or 500, whatever you feel comfortable doing every day. Then stick do it. After a while it becomes just another part of your day.
Or if you don't like the idea of word limits, try this - tell yourself that you're going to spend five minutes a day on your current story. That's all - just five minutes. As soon as you start writing just tell yourself you're only going to be there for five minutes. If nothing comes out after five minutes, nobody can fault you for trying - try again later. Most of the time you'll start off slow and then start to fly. From there you can impose a word limit if you want, or just go naturally.
If you find yourself having a bad day at it then don't worry. James Joyce, arguably the best sentance by sentance writer of the twentieth century was reputed to spend months labouring over each sentance. Steven King had a massive case of writer's block mid way through The Stand. Read any great writers biography and you're bound to discover that they've been in the same situation as you more than once.
Also remember that the best writers write using their own words. Don't be scared to write simple, using everyday phrases. Read some George Orwell or Charles Bukowski, two fantastic writers that crafted beautiful stories by using the first words that came to their heads.
Just keep at it and above all else, enjoy yourself! Writing shouldn't seem like a chore. If you come to your work excited then you'll find that words come a lot easier. Everybody has bad days, but if you stick to it and don't give up then you'll quickly discover that your good days outweigh your bad ones.
Hope this helps you out a bit!
