backlight stopped working after screen fix

Hi all. I'm hoping somebody has a miracle answer for me!

I have just finished replacing a cracked screen on an ipod touch 4g and it was working fine, full colour, touch functions, all buttons... the lot! I left it plugged into my pc to charge and on my return an hour later the backlight was not on. It had remained motionless during this time and i'm absolutely stumped as to why this has happened. If i shine a light on it i can just about make out the icons on the screen, and everything still works fine.

things i have tried:

resetting all settings in settings>general>reset,

holding power & home until apple logo appears,

restoring via itunes (now on 5.1),

plugging in the old cracked screen (which is also dim and wasn't before),

reseating the LCD cable on the board,

checking to see if any pins are missing on the LCD connector on the board,

Could anybody enlighten me on why this could have happened and if there is any resolution? i'm currently letting the battery drain to zero to see if that helps...but it's going to take a while!

thanks for reading