Yeah, I feel you. All I can really suggest is to keep trying to work on your projects. With me, some days it will start to click after a few paragraphs even when I thought I had no will to work on anything. Shifting to some other aspect of the job can help too: go back and do editing, or work on plot outlines for some other project.

Neither approach works very well though. I've spent a lot of nights staring at a blank screen. =/

I understand where you are coming from on that all too well. There have been many times where I will write like crazy for a brief bit, followed by long periods of "........."
Most of the time, it's a lack of motivation or energy, like you described.

One thing that can help is setting aside a bit of time each day, just for brainstorming ideas. Seeing if something decides to take root and make something happen. Sometimes, all it takes is one little seed to make magic happen. ^.^

First, are you getting enough sleep? Maybe too much sleep? When I get into the writing groove, it's like an unstoppable train; only the early morning sun and the job's calling can interrupt it.

How about food you eat? Maybe you eat too much sugar, maybe too little. Maybe you need some dietary supplements? The brain is a part of the body, not a separate entity. It shares the same blood supply, has the same lymph system connected to it, and also takes a third of your basal metabolism. I could say that it's your body which writes stories, not just your brain. Also, there's the other brain in your tummy, which handles the complicated process of digestion has a really big influence on the top one. Sometimes the top one just disconnects, sometimes the bottom one turns off letting the top one wander. Try to be quiet and listen to what the other brain is telling you.

I was in a similar situation; I had rough times on my job, was working non-stop, too much responsibilities, too much projects. For almost a year and a half I haven't touched the (digital) pen. How I got over it? By learning how to relax. Your muse is a nocturnal, easily frightened animal. You can't write if you've been thinking about not writing all week. There should be no pressure. If you can write, okay, and if you can't then it's okay nevertheless.

Another technique is to just type whatever comes to your mind, and don't stop until you fill a quota. Even if the story text turns into a bunch of sorry paragraphs bragging about your life. Don't stop typing. That's one way to lure your muse out in the daylight.

Next, try to read as many different books as you can find! That always worked for me. I find a good book or a story on the Net, start reading it, then halfway through I get angry at myself for not being able to write as good as the author, and that unsettling mixture of shame/guilt/envy works on my muse as a laxative. She comes out running out of her hiding, and before she reaches the outhouse I catch and interrogate a couple of excellent paragraphs from her.

Last thing, you can try finding a writing wingman: someone to keep an eye on your writing progress, help with the story, and encourage/slap you every time you falter behind the schedule.