A couple of things that are easy to try on a mac are to reset the SMC and PRAM. Most likely neither will fix the problem but sometimes they will. You can reset the SMC by removing the battery and power from the laptop, then with no power hold the power button for about 30 seconds and release it. After doing that replace the battery try to turn it on. Resetting PRAM is done by holding the P, R, command and option keys as the computer is turned on. Hold them until after the chime, if it gets that far. Like I said most of the time these two solutions do not fix the problem but are quick and easy to try.