Help!MacBook Wont turn on after Screen Replacement

[musafir]

hi i just replaced the macbook screen as mine was cracked macbook was working with external display perfectly, i should mention i am not a novice have replaced screens on several macs for friends and family never had a problem, but i have no idea whats going on with my own at the moment i have triple checked the connectors all OK,
macbook turns on screen flashes for half a sec and then nothing i can hear the hard drive moving, front led comes on, the optical drives makes a sound as well
i am completely stumped any ideas, i would really appreciate any suggestions at all, i am really really stuck as i have tones of data that i need on this macbook

 

[eman]

When you turn on your macbook, take a bright flashlight and shine on the screen and see if you can see the desktop. Sounds like your macbook is turning on, it may be that you can't see the desktop. When you start your macbook, does the white light on the front of your macbook turn on, then off?
Your data can be retrieved with target disk mode, if it's just a problem with the LCD not lighting up.