Hi @myrah ,
With the camera turned on, try shining a torch at an angle close to the LCD screen and check if there are any images visible at all. They will be very faint so trying this in a darkened room may help to see them if they are there.
''If there are images'' then there is a backlight problem with the LCD screen. This could be due to a faulty screen flex cable connection (at either end, screen or motherboard), a faulty LCD display or a problem with the motherboard.
''If there are no images,'' then it may be a faulty LCD screen flex cable connection (at either end, screen or motherboard), a faulty LCD display or a problem with the motherboard.
I realize that the possible causes of the problem are the same for both scenarios but if it is only a backlight problem and replacing the screen doesn’t solve it, then you are one step closer in troubleshooting the problem on the motherboard by knowing this.
I don’t know the camera but I think that the EOS 750D is the same as a Canon Rebel T6i as they share the same [http://gdlp01.c-wss.com/gds/4/0300018254/01/eos-rebelt6i-750d-im-en.pdf|user manual] and also use the same [https://www.ebay.com/itm/Repair-Parts-For-Canon-EOS-750D-EOS-Rebel-T6i-LCD-Display-Screen-Touch-New-/152637196225|LCD screen]. (supplier example only)
If you wish to try it here’s the ifixit [guide|106320] guide that shows how to replace the LCD screen in the camera. At least you can check the cable connection to the screen and if it appears to be OK maybe replace the screen as it is not too expensive.
If you decide to replace the screen there are other suppliers online that may suit you better. Just search for ''Canon EOS 750D LCD replacement''