When I was really depressed several years back, I actually sunk into being nocturnal. Since I had to be awake for school, summers would actually allow me to be awake at night, and asleep during the day. Believe it or not, I found that it actually worked pretty well to get my "night" of sleep from about 6 or 7 pm (after I got home from school) until about 3 am. Then I'd wake up and do my homework.

That may or may not work for you. I'd recommend increasing physical activity during the day. That'd make you tired at night and more ready to sleep. If there are other activities you know that put you to sleep, go for it. I used to fall asleep on my Gameboy. Not the best position to fall asleep in, but hey, it worked. Reading sometimes works, relaxing music... anything, just make sure it's something that works for you. Maybe a tape of a history lecture? I couldn't stay awake in one of those if I tried XD

Good luck!