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The obvious simple possibility is that the 'Brightness' control was turned down. If you press and hold the F3 key down. Does the screen brighten? If it does, that's about all there is to it. Otherwise...
If it's under warranty, check for how to get repair service. If you're not comfortable diagnosing, buying and replacing parts, ask a local qualified PC repair shop what they can do (and how much it will cost).
It seems likely to be some component part rather than anything that can be reconfigured. Regardless, it's very likely that no one can do anything about it through an internet forum. The laptop probably needs to be physically available before an actual problem can be determined.