Problem with the screen of a Dell Inspiron 1521

Question

I purchased a Dell Inspiron 1521 in December 2007.

I'm having trouble with my screen, where it turns blue with red lines and as sometimes changing it's position fixes the problem, there's others where it wont go away (which is the case right now)

I´ve try connecting an external monitor and the external monitor does not show the same problemI appreciate your assistance with this matter