OK I opened it up and I couldn't see what the problem was. Nothing appears damanged, as expected. There are three main ribbon cables, none of them appeared loose. However, when disconnecting the mainboard from the phone case, the middle cable, which lights the LCD screen, has become fully detatched. It seems that unlike the other two cables, it connects via adhesive. I don't have thermal adhesive. When the phone turns on, now there is no backlight in addition to nothing being visible on the screen. PC Companion picks up the phone so all of that seems to be working. But no LCD and now no backlight. Unfortunately, there is evidence of me opening the phone. I doubt the warranty would be accepted now...?
In the reassembly video in document 1277-1354_Rev1 , it shows the three connectors just snapping/connecting....no glue situation.
If there is anything else I can do via home repair, what could I do? I can't be that far off, surely?