1. was there any overheating? dropped your laptop? poured coffee on it? other possible hardware damaging activity?
2. do you hear the HDD spin when you turn it on?
3. if you screen doesn't light up, how do you know keyboard won't work?
4. does the sound work?
it could be a few things
1. motherboard faulty
2. lcd faulty
3. connection to lcd from GPU faulty