Troubleshooting: Keyboard stopped working and Windows won't boot past loading screen?

[astroidea]

I placed my laptop onto my bed gently and suddenly it shut down. Afterwards, I rebooted. After windows loaded, I get a blank screen instead of my login screen.
I tried going into recovery mode and noticed my keyboard didn't work even though the power button and the trackpoint works. The keyboard doesn't work for going into BIOS either so it's not a software issue. I hooked up an external keyboard and it worked although windows still wouldn't successfully load.

This happened about a week after I took everything apart to replace the thermal paste after I was getting overheating.

I tried reseating the keyboard connector with no help. But what's really baffling to me is the co-occurrence of the keyboard issue and the windows loading issue.

I'm guessing this is a hardware issue. I'm wondering what part I need to replace. I'm guessing either the keyboard or the motherboard.

[RealBlackStuff]

I placed my laptop onto my bed gently

which probably blocked all the vents.
No fresh air coming in, no hot air going out, most likely CPU died from overheating.
Try another CPU (if not soldered) and check that the fan still turns...

[astroidea]

It shut off right when I placed it on the bed so it seems like the shock, however mild, loosened something. It wasn't overheating. I've been really mindful of the temperature especially since I replaced the TIM.

The fan still works and turns on while it's booting. The CPU is soldered, I have the T420S.

[RealBlackStuff]

Maybe HD/SSD 'roaming' without bumpers? If so, correct and reseat.
USB port(s) damaged inside?
CD-drive not quite in?
Keyboard/trackpad connector loose?
LCD-cable fallen out of LCD or loose inside?

[astroidea]

Windows still boots. I just get a blank screen right after it loads.
It's weird that the keyboard doesn't work but the trackpad and power button works.

Anyways, I saw a replacement motherboard on ebay for $25 shipped with nvidia graphics. This will be a good reason to upgrade.

[astroidea]

The new mobo didn't fix it. But I found out the issue. The lid close sensor was triggering with the lid open. Somehow, when I loosen the screws on the bottom of the thinkpad, the lid close sensor works as it should. I need to find out where the lid close sensor is and figure out why it's activated when there is too much pressure applied to it from the screws.

[RealBlackStuff]

The magnet sits under the palmrest, near the front, left of the bottom-mouse-keys-opening.
See second picture, the silver square with a cross on it: https://www.ebay.com/itm/172884832333
The sensor is inside the lid, near the webcam, matching/opposite of that magnet.

[jaspen-meyer]

Quoting the HMM:

Tighten screws as follows:
• Plastic to plastic Turn an additional 90 degrees after the screw head touches the surface of the plastic
part:

• Logic card to plastic Turn an additional 180 degrees after the screw head touches the surface of the
logic card:

[astroidea]

I just fixed it. I think it was due to the cable that connects the camera/light/hall sensor not being tucked behind this structure. It instead was resting on top of it which put a lot of pressure on it with the screws tightened.
I also tightened the screws on according to the info by jespen-meyers.