Just because the screen is not cracked doesn’t mean that there isn’t an internal problem in the screen (e.g.broken connection) due to the fall.
With the phone turned on, try shining a torch at an angle close to the screen and check if you can detect an image at all. It will be very faint if is there at all.
If there is an image there then there is a problem with the backlighting in the screen but this could either be a problem in the screen or the systemboard
As a DIY repair to prove if the screen was faulty or not you would need a replacement screen that you could temporarily connect to check whether it is the problem or if the problem is in the systemboard
If there is no image there then phone would have to be opened and inspected as to what the problem may be.
Either way the phone will have to be opened
Here’s a link to a video that shows how to replace the screen in the phone which may be of some help.
If this is too daunting a task, contact a reputable, professional mobile phone repair service and ask for a quote to repair the phone.
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