I don't know any sure fire cures for writer's block. It's something most writers go through in some form or another, and there's no easy answer for what can make it go away faster. If there is an easy answer, somebody tell me because I'd love to know. :)
Writer's block can mean different things to different writers. Basically I think writer's block is anything that keeps a writer from writing. (Not including circumstances outside our control like...your computer crashing or having a weeks worth of work that just doesn't allow time for anything else, etc.)
There are two main types of writer's block that I've had. The first is the type of block where you're stuck on a plot point or you can't figure out where a story is going. The second is when you pretty much know what you're going to write, you just can't seem to get up the motivation to sit down and do it. The first type, is I think easier to deal with because all you really have to do is figure out how to fill in your plot holes. You can work on that, and therefore be working on your story, even while you're not doing the actual writing of your story. The second type, on the other hand, involves a lack of motivation that is harder to pinpoint and solve. It's not like the first case where you just have to figure out an answer to problem; it's fighting with your own internal apathy.
So if you are blocked, what can you do about it?
Well, in the first case, where you have a plot related problem, you should be trying to figure out what will make the plot work. Sometimes it helps to make an outline, maybe you could make lists of the plot elements that are bothering you and see if something pops out at you, maybe you could make a chart...whatever helps you see the structure of your plot might help you see how to fix it. And writing things down is one way to keep yourself thinking about your plot, it brings it to the forefront of your mind and focuses your attention on your story, so even if you aren't able to fill in the holes in your outline, at least your mind is considering possibilities. Other things to think about when you're trying to figure out a plot hole...character motivations, your purpose in writing the story or the point you're trying to make, specific scenes you plan to include and why they're necessary. Sometimes looking at something like a character motivation will help you figure out what your villain or your hero would do, how they would act, and knowing that could give you the scene you need to fill in a plot hole.
Talking to someone can help. Anyone you can use for a sounding board, be it friend, parent, teacher, whoever, will do. A lot of times for me, just describing the story and explaining the plot to someone helps me see new possibilities. If your person can give you suggestions that's even better...they may not give you a suggestion you can use, but their responses may give you a new idea or spark something for you. If nothing is working, you may have to just put the story aside and wait. This doesn't mean forget about the story, it just means...it's possible that you need a little distance from the story to figure out what needs to happen. So think about it, brainstorm, but don't force it. Know when to set it down and just go do something else.
Another thing you can do if you're stuck is jump ahead to a part of the story you're sure about. I, personally, don't do this. I need to write my stories in sequence to let things flow and develop as they go. But I know other writers you will write whatever parts of the story they imagine at the moment, be it an ending, a piece of dialogue from the middle, or whatever. If you're afraid you'll lose momentum when you get stuck, and you don't want to stop doing the writing work on a story, then moving to a part you aren't stuck on and writing that might help.
If your problem isn't a plot hole, but a lack of motivation there's less advice I can give. That's a much more personal problem and could be caused by any number of things. I'm a terrible procrastinator, and I have problems motivating myself to write. What I try to do is write some fiction everyday. If you're working on more than one project and you get blocked on one, maybe you can work on another for a while. If you've just got one project going, try to write something, anything, everyday. Even if it's only a little bit of writing, even if it's not any good. Once you get something written, you can always go back and revise it if it's bad. But if you just let it sit without working on it, the longer you let it sit, the harder it will be to get back into it. I find it's much easier if I maintain the creative momentum by pushing the story forward every day, even if I'm only pushing it ahead by inches.
Of course, sometimes you may just need a break. And if you do, then certainly take one. But try not to let it become a constant avoidance. I've found that if I allow myself to keep putting something off, and saying...of I'll write that part tomorrow, tomorrow, tomorrow, then it takes a really big effort to force myself to actually WRITE. By the time I do, it's like I'm in the habit of avoiding writing instead of being in the habit of writing.
I will also say this. Sometimes you don't feel inspired. It's your choice during those times whether you want to wait for inspiration to strike or whether you want to press on. But I do think, at least for me, writing is as much about work as it is about inspiration. You need to have some sort of inspiration to come up with an idea for a story in the first place, but to actually write the whole story, iron out all the problems, write and revise...all that is work. Don't get discouraged if writing your story feels like work...you're not doing something wrong :) Just keep trying, push yourself onward. In most stories there will be parts you breeze through and parts that drag. Don't let the draggy parts keep you from finishing.
The fact is, everyone has different writing methods and it's really up to you to find the best way for you to deal with writer's block. But it's good to remember you don't have to stop working on your story when you have a block. You can work on perfecting your ideas, you can work on another project to give yourself a break, or you can press on despite a lack of inspiration.