Writing is more than the bit where you sit down and write, you're always 'writing' just by thinking up stuff. Feed your brain a few bits of information relevant to what you're doing ("Geoff thinks he's got two months to live, how does this resolve itself by the end of the episode, bearing in mind subplot B where his boss is coming to dinner and his wacky ex-wife neighbour has borrowed his... SOMETHING") and let it percolate, go and do something else, and you'll get the answer a few days or hours later (thanks to the wonder of your subconcious). Then you just write down the story that already exists in your head, as though retelling a story to a child at bedtime. (No one actually ever does this of course. Even though this is the guaranteed way for me to overcome a block, I still stare blankly at the page/the internet in a panicky rage for a day straight, until I get up and do some washing up and the knot unravels itself immediately)
If you're REALLY stuck for inspiration,take an existing story and update or rewrite it in your own voice- worked for Roxanne, 10 things I hate about you, West Side Story etc. The hardest bits been done for you then.
If you're really stuck on where your characters can go or if you think you've mined a topic to pieces, draw a chart. Put People, Places, Things, Events, and Cliches across the top of the page, and write in the appropriate things you associate with your subject matter. (Gene Peret, Carol Burnett's writer, uses this in his book Comedy Writing Step By Step and it's incredibly useful for mining every possible joke or observation from a subject.) He uses the example of his dog, so under people you have: Pluto, Lassie, Pavlov, The Vet - all people you associate with dogs- under places he puts The Park, the Kennel, The Dog House, under cliches you have 'Man's best friend' and so on. THEN when you've done that, make a new row and go through the columns again adding opposites or negatives, ie the opposite PERSON to a dog is a cat, and opposite PLACE for a dog is a china shop, or allergic person's house, an anti-dog CLICHE is "I'm not a dog-person", and so on.
You end up with a huge list of subcatagories on this one topic, it's damn useful.
Hope this helps.