Here's an easy fix I just did...posting it in case it can help someone in the future...
Got a 15" dell LCD that would turn on then the screen would immediately go dim, but the power light would stay on...shined a flashlight into screen and could see screen was still on, just no backlight....
opened it up and checked the inverter circuit on power board....found a blown cap(it was bulged actually)...16v1000uf variety...replaced it and voila...screen works perfect again...yay!
Upon doing some research found out this is a pretty common problem(tons of folks have this problem on fixya) not only with dells but with lcds in general, so thought I would post it up...here's a pic showing the cap in question on the dell board...

I believe it's caused from excessive power failures...like building loses power and/or gets surges a lot...just my theory...
Hope this helps somebody some day

On a side note...since i quit smoking i have entirely too much free time lol