The only way to get to your HDD is by removing the top layer (keyboard + touchpad), just make sure that you put back correctly the touchpad wires, even if it looks good but still not work retry again because the problem is there, make sure not to break it and good luck :).
It looks like your SSD is dead and recovering your files will be an impossible task as far as I know, to be sure, you need to plug it in a desktop PC and see if he can recognize it, avoid any further booting attempts to prevent additional damage.
Generally, lamps and other accessories are connected in groups sharing the same fuse, so if there a problem with the fuse then you’ll notice it in different areas, I know this will sound a little bit weird but have you bought the right lamp model? If you don’t know then compare it to the old one and to be sure that the lamp is working fine, you can test it directly with battery.
First, we need to figure out if you have a power supply issue or an APU issue which you can verify in this video. Also, you can take a look at this post maybe you find an answer. PS4 not turning on (no light, no beep)
Hello, I really don’t think there is a way to solder the ribbon cable because the wires are very thin, close to each other and they have to be covered with an isolator material like plastic to prevent them to touch each other.
I don’t think that this kind of device have any protection for overvoltage because generally the protection system is integrated into the power supply, but in your case, you directly connected your tablet to the wrong connector so you damaged the motherboard, I didn’t find much information about your model and to begin with, you have to take a photo of your motherboard and focus on the area around the charging connector, you can watch this video to help in the disassemble process.
You have an overheating problem, there is a safety switch that shuts down your computer immediately when the CPU overheats, the first time when you turn on your laptop, your CPU is at ambient temperature let’s say 25°C then it jumps to around 100°C and trigger the emergency switch, in the second try your CPU is no more at 25°C but somewhere around 90°C which means the CPU will reach the threshold temperature (100°C) much faster. In order to cool down properly the CPU, you have to check first your fan if it’s spinning or not and clean up the radiator.