HELP!! Screen problems

I have a Studio 1555 and have owned it since early 2010. However, exactly one week ago my laptop's screen all of a sudden went blank.... there is a huge blank white spot on the screen covering up about 3/4 of the screen. It's hard to describe... I have not been able to use my laptop in a WEEK and am desperate to know why this would all of a sudden happen....  And it's stayed like that for a week....