problem with laptop screen?

my laptop screen is always flashing and sometimes goes really dull, to the point at which i cannot see the screen. i have to partly open and close the laptop until it stops and then a few seconds or minutes later it starts flashing rapidly again. i have sent it off to be repaired and it worked fine for a short while. what do you think the problem could be and how can i fix it?

ashley w
December 2010