What would cause my screen not to come on?

This is happening more and more often. Sometimes, my screen will not come on. It is not the brightness adjustment, I already tried that.

Then I noticed that if I shine a light through the translucent Apple logo on the back of the cover, I could see the part of the screen that is across from the Apple logo. So, I assume there is some backlight that illuminates the screen.

Some other relevant information: last year I dropped the MacBook and broke the screen. I sent it into www.macservice.com for repair. For $300, they replaced the screen, but after I got the computer back, there was a new, annoying buzzing sound that would vary in volume whenever I change the screen's brightness. Also, the iSight camera would no longer come on. Could this be related?

So what part is it that is failing now? Is it separate from the screen?

I've done things in the past such as change memory, hard drives and keyboards in the laptops and iMacs and Mac Minis that I have owned.. So I may try to fix it myself, if I know what I need to replace. I won't send it back to macservice again. I contacted them about the new issues when I received the repair back; they said they would issue a new RMA and send me FedEx material, but they did not follow through.

Any insights, advice, suggestions, etc. will be appreciated!

Thank you.