I've had this problem with my dell latitude c610 for almost a year now. I've just recently had alot of free time on my hands and the motivation to finally get it solved. Whats happening is the LCD screen is very dim (almost completely black) on some power-ups, but not on others. And sometimes the screen will turn on dim and remain that way through the dell and windows splash screens but then it will kick back to normal once windows loads.
You'd probably think that this would be a very annoying thing to deal with for a year, but the thing is i've discovered a kind of "half" solution. If the computer boots up and loads windows with the screen still dim, I shut down windows and remove the AC power cord from the back of the laptop. Then I power up again, and the screen will always work
properly once windows loads. I can then plug the ac back in and get some work done.
I've installed the newest video drivers from dell and I even updated the bios from A07 to A16 and the problem persists. I've booted in safe mode and the problem persists. But after reading through past questions I've realized it may be the backlight or inverter is going bad. I've found a website that sells backlights for cheap http://www.lcdpart.com/doc/ccfl.html
but I don't know if its advisable that I try to install it myself or not.
Well I think i've covered most of the background, i'll probably think of somethign to add later. Thanks in advance for your time and help.