My Sony laptop is in darkest contrast and the screen is black?

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I was messing around with the display and I put my contrast display into the darkest so now my latop screen is black and I can't see anything but the laptop is stll running. It's a Sony vail laptop and there are no switch to change the contrast and I saved the change too so even if I turn my computer on and off it's still black is there any button I can push so that my display goes back to normal????please help I already tied pressing the numblock button an then the one with the sun and the plus sign and then I tried pressing the fm buttoon and then the one with the sun and I tried pressing them Both together at the same time nome of it worked I am currently typing on my iPod so pleassee helppp