Lava lamps are odd, temperamental creatures, but beautiful in design. So easy! Thermodynamics rule! Little blobs of wax (a paraffin/mineral oil composite, according to stuff I've read online) get heated up and float through the solution up to the top, cool off, and float back down to do it again. (The wall socket one I have works on the same principle, though the things heating up there are flakes of glitter, not blobs.) The light bulb in the lamp doesn't directly heat the goo, though; it heats a metal coil in the solution which touches and heats the goo as it comes down to rest.
Nice and simple, but if the metal coil isn't firmly located in the bottom of the glass globe, the lamp may refuse to, uh, lava. When I brought the lamp out of the box, I saw that the coil had become encased in the hardened goo and rested along the side of the glass. That's what makes 'em cranky. I'm also guessing the ambient temperature around the glass might make 'em cranky, too, cause when I lived in Marlboro I had the lamp by a drafty slider door and some times it refused to play at all, and I'd have a big lump of red stuff at the bottom of a lamp. Like I said, they're temperamental creatures but when they want to show off, they do it nicely.
You can't shake the lamp to dislodge it, at least, not very hard, because the goo stuff likes to separate and then you get little tiny goo dots instead of nifty blobs. I've got a few in my lamp. So tonight I heated the lamp up a bit and then took the glass bit off the heat and tilted it a little and tried to roll the lamp around to get the coil to stick down. (Don't do that with bare hands, by the way.)
Everything seems normal now and I've got a lava lamp happily burbling away behind me, giving the room an eerie glow. If you watch closely you can even see the light level in the room rise and fall, too. It's rather nice. Everything else might be going to hell tonight, and I've been learning throughout the course of the day that everything I know is wrong (cathartic, yes, but always a hard lesson to learn) but at least my lava lamp is working.