Don't know what skinny boards up top mean.... photo would be nice.
Check the photos i attached; you'll need to completely release the clip that locks the ribbon cable in its socket. 2 red arrows point to where you should LIFT the clip 90 deg upwards. 2 blue arrow point to properly inserted (properly seated) ribbon cable.
Second photo has one red arrow that points to the ribbon cable "prongs" that should lock in to corresponding dents in the socket BEFORE you lock the long, black plastic clip.
If you still have the same problem after you've re-seted the cables (both ends: one is between AV processing board and T-CON, the other end is between T-CON and LCD panel) -> it is most likely a TAB issue, check the third photo that points to defective TAB's....
Re-seting the cables will break contact resistance that is common cause of the problems, in particular with such a small contact area / high contacts' density + bare copper contacts that WILL oxidise with time.
Hope this helps, good luck