Hello I had this problem already multiple times with my 2x Vostro1000.
Just open the panel which contains the powerbutton (and some light indicators).
Under that you will find the backlight inverter to your display. press the 2cm long connector back into its connector-slot (around the location just above the 'printscreen button'.
It seems that the design of the connector coming from the backlight inverter is poorely made.
I always push the connector back down and it's OK. It's like a 2 min job.
I learned this from another guy who had the same issue with Vostro1000.