I can't necessarily provide specific advice, but what you need to analyse is:
1. Where are the barriers to starting, how can you lower these.
Many people don't even get to the doing part, they put off starting a task. By making it easier to start it makes it easier to write for a few hours.
I.e. I have (personally) tried a bluetooth sliding keyboard, found pressing the keys to be awful, purchased a stand-alone bluetooth keyboard that works with my phone because it was much nicer to use. (don't let "waiting for the new keyboard to arrive" be an excuse)
You may find that you get hungry/thirsty after a while of writing; and thats the biggest thing stopping you, consider having available food/drink.
2. what are the major distractions that you can get rid of, or would like to work around.
You have identified sound and internet already. but you might need a comfortable chair too, or a light enough workspace so that you dont fall asleep, Or to pay the bills you keep putting off because they won't leave your head enough to let you think of the story.
Consider also making a list of things to do after writing, then leaving it in your way away from the computer so that when you are done with writing you can get straight onto that list, but while you are writing it won't matter to you because its written down somewhere.
Some people are distracted by sound, some people are distracted by mess, some are distracted by having books around in the library. It really depends what is distracting you and whether the "distance and time to the library" is worth it (it might be). Or also "the house is too mess and so I am going out" might be more easy than staying home.
3. is it in your diary/calendar?
Regularly marking time out to do X will help it actually happen. trying to fit it around other things, especially a long standing project without the same new project motivation is going to be difficult to convince yourself to start X today
I assume you already have a plan. (the plot thing) So "knowing where you are going" is covered.
You may not need to fully disable the internet, an option that seems to work for some will range from any kind of serviceblocker (i.e. facebook limiter program) to the cat5 plug across the room. by raising the barrier to starting the internet and getting down a distracted path you lower the chance you will do it unless you really really need to.
Also having good check-habits will help. i.e. whenever you leave the computer you make sure the internet is off; so when you come back you can start with writing specifically, rather than starting with facebook.
Something like a word-count written in big somewhere (whiteboard, on the door, on the ceiling above your bed) might help you feel like the progress is serious and relevant. (word count may not be your goal, rather plot milestones, some kind of indicator to yourself)
Consider time tracking - i.e. rescuetime. It has a pretty useful free version for keeping track of if you are genuinely using the word processor and/or knowing what you are mostly using as a distraction/largest chunks of time abuse.
How many hours do you think you have left of the project? Then divide this up by the number of weeks left.
If these have helped I probably have a few more.
don't let "waiting for the new keyboard to arrive" be an excuse
I'm planning on not, either in the specific case or in general. (Which is why I went for my precommitment yesterday.)
(In case you're curious, my external keyboard is the one shown at http://www.dx.com/p/convenient-69-key-wireless-bluetooth-folding-keyboard-for-tablet-pc-smartphone-black-303707 ; fits in a pocket, allows full-speed touch-typing.)
available food/drink
I've already got my backpack ready for my first writing-focused trip to the library, come Tuesday: my preferred car...
Yesterday, I set a personal deadline: If I haven't started writing more "S.I." by Canada Day, then I'm going to start writing up the fast-finish version of the plotline to at least tie up the story and stop having it hanging over me.
Never underestimate the power of precommitment.
Now that I've started thinking in terms of my writing more of SI as a simple fact, I've realized that, due to complicated/personal/private home-life stuff, in order to actually have a reasonable chance of even writing the short ending, I need a new low-distraction work-space, and nowhere in my home is suitable. The most likely candidates are my local public library when it's open (Tue-Sat, 10am-5/6/9pm), and, elsewhen, a particular local coffee-shop with a customer-available power outlet. And, in fact, my not noticing the lack of a suitable low-noise typing location may have induced an ugh field that kept me from even trying to catch up with suggestions and comments to SI even as my depressive episode has waned.
It occurs to me that there may be further options I'm not considering; and that there may even be other aspects to the process of writing which could be hindering my progress. And so, I come here, to inquire of the local hivemind: What advice can you offer?
For example, I currently have two and a half devices to type with: A Thinkpad laptop, an iPhone with a touchscreen keyboard, and an iPhone with a (folding) full-size Bluetooth keyboard. Should I look into some other input device?
Or: Is there some aspect of nutrition or hydration that I should pay more attention to?
Or: How significant is the audio environment? Should I pick a particular soundscape or playlist and hook up the headphones, or would there be minimal effect compared to a library's shuffling or coffeeshop's satellite radio?
Or: Would turning off my connection to the internet, save when I'm looking up some reference, be useful or annoying?