Laptop not turning on, behaving strangely instead

[JurkyB]

I will write every detail that I can in the second part, but here's a summary.
I have a Samsung laptop, which is 4 years old. I disassembled it today, to clean it, and built it back. It turned on wonderfully, everything worked. Then I restarted it, because it said that it should update. Then it just doesn't turn on, not even BIOS or anything, just some strange shapes on the screen, here are links to see them:
http/i.imgur.com/CiUjODB.jpg
http/i.imgur.com/TG0MPpZ.jpg
http/i.imgur.com/FqM0VsQ.jpg

And now the description with all the details (some might not be necessary, but they might be useful anyway):
The laptop is a Samsung NP350V5C
It has win8.1
It didn't have any issues whatsoever in the last 4 years.
I disassembled it, had some issues (a connector didn't want to be unplugged, so had to it without, but it is just the speakers, which remained fine afterwards). Then assembled it back again, turned it on, and the screen was weird, half of it was made out of white squares, the other half nothing. It was that way for 5 seconds, then turned on just fine. It worked like a charm, maybe even faster than it was before. Turned on music to see if the speakers worked, and tested the usb and other plugs as well. Did not have any issues.
Then I saw that it should restart to install some updates. I restarted it, and it began updating. I checked back after a while, and it had these weird things going on on the screen (haven't seen them before). Waited, then made a forced shutdown by holding the power button, even removed the battery.
After that every turning on is the same with these images. It's not just a freezeframe, it's constantly changing, and even flickering at some places. The computer usage indicator led (I don't have a clue about it's proper name) is sometimes shining sometimes not.
I checked the laptop and noticed that something was hot in it, even if it only ran for about 10 minutes. It was the HDD. After the next powerdown I unplugged it to see if it was anything else without it, but nothing changed: these images were still there, and the laptop still wouldn't respond to anything.

I would really appreciate any tip, trick or something. If you need more info about anything, just ask here.

Thank you all in advance guys!

 

[Fallonite]

This sounds like an issue with the built in screen on the laptop. Maybe you either disconnected something or you bumped something inside to damage it. I would recommend going back inside and making sure no cables are loose or broken.

If everything appears fine to you, I suggest either taking it an to an experienced laptop repair shop, or just buying a new laptop. Those are really the only two things you can do if nothing appears loose or damaged to you.

 

[JurkyB]

There's an HDMI port on the laptop which is right on the motherboard, and if I connect it to a monitor nothing happens. Also I failed to mention that after 5 minutes the screen turns off, and if I tap the touchpad or press a button then it turns on.

 

[Fallonite]

It sounds to me like the laptop turns on and boots to Windows, but the screen is damaged or corrupted, possibly due to heat actually damaging the connectors, as well as damaging the HDMI port.

If your laptop is suddenly overheating, it could be that when you went to disassemble it, the heat pipes were nicked or bumped or otherwise moved, or possibly one of the fans was connected back the wrong way. I would go in and double check and make absolute sure that everything is how connected how you remember it was and that nothing is damaged or has any dents or bumps.

 

[JurkyB]

So I disassembled it, got almost every cable out of the sockets, plugged them in again and now it works just like before. No more squares on the screen, nothing strange. Maybe it was the connector to the screen, but not sure because it was reacting somehow to what I did with the computer and the HDMI connector didn't work either.
Thanks for the tips.