One possibility is that the backlight in the screen has failed, but the LCD panel itself is fine. Try viewing the screen under very bright light, or shine a flashlight at an angle from the side to see if anything is visible on the screen. If so, then replacing the backlight should be all that needs to be done, provided you can still find a compatible replacement.

As for the ribbon cables, I have no experience with this, but I've seen other posts on here before where people have been able to cut off the frayed end and strip off the coating to make a new fresh end that fits into the motherboard connectors properly. This may work, provided there's enough slack in the cable to do so. Again though, I've never done this before, so I'm not qualified to give technical details or further advice on such a process.

Thanks for your advice torin, I'm waiting for a friend of mine, he's more able than me with surgical operations like this - I guess also the coin battery will be to remove/change, of course... it is soldered 🙁

So, change the backlight isn't that difficulty? Is there anyone in the forum who has done this before?

I should correct myself and say it's typically the voltage inverter that powers the backlight which could have failed, and not the backlight itself. I have replaced the inverter on a few modern laptops, it's typically not a difficult task and I would assume (but cannot guarantee) an older laptop like that would have similar construction and replacement methods. My earlier caution still holds true though, finding the correct inverter for that specific model of laptop may be difficult since they're not a universal part.