LCD Backlight does not work!

My problem began with a "no airport card" issue that came up from nowhere. I ordered an airport card and replaced the one I thought was defective with the new one. I finished assembled everything back according to this MacBook Unibody A1278 Once done, I powered up my MacBook. To my surprise, the screen was not lighting up. I first thought it was dead but upon a bit of luck, coincidence and research, I held up a flashlight and saw it was working. Since then, I have tried researching everything about this model (A1278) and have yet found an answer. I don't know where to look and therefore don't know where to start solving this second problem. I also connected the MacBook to my external monitor and hardware wise (except airport card and backlight), functioned correctly. I'm short on money right now so I don't have the $$$ to send it out for repair. I usually perform all my repairs on broken items (I don’t usually break stuff).