when you say it is dimmer than before, is the backlight coming on at all, or is it not on? because they would be very different. If you can adjust the brightness and it is visibly illuminated, just dim, then there is a fault with the machine, because everything is connected fine. Whereas, if you cannot see a backlight but can see the image faintly (either with natural light shining on the screen or looking with a torch) then it is most likely the connection of the inverter board that is not seated properly.
either way you will most likely need to open the machine back up again. I'd initially check all the connections, then if it doesn't help, you will need to track the fault down a bit further.