Like Aaron said it's probably the bulb. Keep your receipt if your going to buy pet bulbs as they are hit or miss, touchy anyway. You can use a black bulb from home depot or a bulb dealer on Amazon as long the wattage you need is there. The deep domes help focus the heat, don't give up on them yet. Old school timers help too.

I touched one of the screens on top of my cage one night with the very tip of a 150w bulb I had installed 30 seconds before. Quickest $11 I ever spent (on a utility item).The surge took out the dimmer built in to the cord (Flukers I think). The next day became my first deep dome unit.