From my limited experience that sounds like the LCD screen has failed. It’s less likely to be the cable. I bought a second hand one for a laptop and fitted it myself, you’ll often find a video on U-Tube but I work on the principle that if someone put it together, I can take it apart again. the screws will be hidden by rubber pads or inserts, prise them out carefully! take your time and lots of photos, don’t over tighten the screws when it goes back together.
When I fixed PCs for a living, we were issued with wrist straps. I used to wonder if it was more about how professional we appeared, given that it was field service in homes and offices. Myself I’d previously either left the base unit plugged in with the mins switch off if needed, so that the case was grounded. You can’t really work inside without touching the case, so you are then grounded too. Back when I was a student we used to use the stainless drainer in the kitchen for our electronics projects. I used to find the strap a pain as it would always catch on things, plus if it isn’t at the tip of your finger I wonder how good it is at getting rid of all the charge. As others have said, it really can’t hurt (unless you catch it on the case) to wear one.