My apologies. Seems like I misread your first post.
So you replaced the inverter, and yet the backlight still will not come on? Damn...
I had the exact same issue. If I shined a flashlight onto the screen, you can see that the image was there. As mentioned, my issue was resolved by replacing the inverter.
If you're taken it apart that far, I assume you aren't afraid of doing a little bit of troubleshooting. If you've got a multimeter, test to see if the inverter is being powered or not. CAFEFUL NOT TO SHORT CONTACTS! If not, trace back the wire. I'm uncertain where your inverter is located, but mine was under the screen bezel. A possibility could be the wire may be damaged from opening/closing the laptop.
If the inverter is getting power, perhaps the bulb itself is burnt out. A quick google search shows me that there is just one bulb in there.
That's all that springs to mind at the moment. Maybe you've got a BIOS setting for brightness you can change that, but I'm almost certain that this is a hardware issue.