Its either the cable Or lcd itself. it also might of just disconnected from either the motherboard side connector Or lcd side.
Guide 1:
View: https://www.youtube.com/watch?v=HBgXV2RLdIo
1. Remove powr cable then follow this guide until 20seconds mark, just remove the battery connector first. Skip until 1min25sec when he removes the LCD cable from the motherboard, this is the cable we are talking about, just unplug it carefully and then plug it back (if it looks fine and not broken anyway) , check that cable is mounted correctly and not been pressed by anything. Keep the battery connector unplugged and put backplate back in , then continue with below guide.
Guide 2:
https://www.youtube.com/watch?v=u1XFFi0jq_Q
2 . You can reconnect the cable on the LCD side and check if it looks fine following guide on this video,
Just do everything slow and be careful with the connector, just take connector off and put it back, check that its fully connected then reassembly the lcd panel and front bazel back in.
After that just open backplate once again and connect battery connector. After that reassembly the backplate, disconnect external monitor connector, and try to boot up.
If it doesnt work, disconenct power cable and then take off backplate, disconnect the battery connector and flip the laptop so screen is on the table and rest of the laptop is pointing upwards. Now connect power cable and boot the PC, try to very carefully move the LCD cable inside the motherboard (dont touch near connector on the motherboard) just to verify if there is problem inside the LCD cable, you might get picture on different position or strange colors, flashing etc. Just move it very slowly so you dont short the connectors on lcd or motherboards end. Then just plug off the power cable, and connect battery connector, reassembly backplate.If you got picture or flashing or something like strange colors something might be pressing on the LCD cable on its way to the LCD, or the cable itself is bad and you need to replace it , if you only got black screen during this procedure then replace the LCD, for that we need to know what resolution panel you have currently.