When i push the power button of my macbook air A1304 (mid 2009) it turns on (the White front power light is on), but no sound and screen remains black: the keyboard is not backlighted anymore. HDD has been replaced 6 months ago, and it can be related to it, since, before, at least the screen turned on. I think it could be related to the main logic, as no sound is heard during bootup. Any tips/help regarding the part that may be failing?