Pretty much all my "songs" are unfinished, I mostly use Nanoloop so I just come up with lots of small ideas and musical phrases and then jam on them live, hence my lack of full releases. Anyway if other people or I like some of those ideas I'll flesh them out to full songs. I don't do that a whole lot but at least it gives me a huge library of material to play live. I find I tend to write the most material when I'm coming up to a deadline
So basically my method for overcoming writer's block is writing (and saving!) lots of small song ideas, no matter how small, and have a reason & timeframe for everything to prevent procrastination and messing around too much (for example: i am writing this song, which is a floor destroying dance track, for my live show this saturday, and i will achieve this by ...). It's also worth coming to terms with the fact you won't like everything you write, you will have off days. Take some time out, no point in dragging out your misery ... unless you have to finish your project soon, in which case inspiration will come, trust me