Screen goes blank randomly while working.

while working on my Powerbook, the screen sometimes fades into a black screen. The computer still functions, but has no usable screen. Most times while pressing down gently on the right side of the palm rest, the screen will come back as long as i am pressing the right side. If i let go, the screen goes back to black. I also have had success sort of twisting and putting pressure on the left side whrere the screen hinge is. When it finally does come back on without the added pushing down, it seems to stay on for days at a time. Then it will go thru periods of going black. What may be the problem, and is there an easy fix for it?