Try not to use the glue… it could be a mess. Try some tweezers like this one. Do it very slowly and remember to disconnect the battery first. Wish you luck!!

It could be a lot (really, a lot) of things that can make your laptop do that issue. So, let´s start with the simpliest procedure: 1- Try taking off the battery and the plug in the power cord and try to power-up your device, if it works, you´ll need to replace your battery, but you can used without it anyways. If the problem persist, 2- You´ll need to take off the RAM memories and try to clean it up( you can do this operation with an eraser, cleanning the golden contacts; make sure you don´t left behind any remains of the eraser in the memory). If you have more than one memory try each independently. If the problem persist, 3- You need to fully dissasembly your laptop and take a close look of the motherboard, maybe (if dirt on it) try to clean it up with a brush and some isopropyl alcohol. If the problem persist, leave a comment so we could continue trying to help you. Good Luck!!

It could be an issue with your Hard-Drive (some sectors might be damaged), you need to check it out with a bootable tool like Hiren´s Boot or a direct boot of HDD Regenerator. Here´s a download link for Hiren´s Boot Restored Edition ,try make that iso bootable in a USB stick (The README folder has a pdf with the How-to). Then boot the tool and check your Hard Drive with: Dos Programs/Restored utilities/HDD Regenerator. If your Hard Drive ends up OK you can make a data safe off all your info with the mini windows in the same bootable tool. And then you can fresh install your Operative System. You can find online all the windows iso files and the serials and cracks if you don´t want to pay for it.

It seems like a motherboard problem, you need to fully disassembly your laptop, and take a close look of all the motherboard, you need to be very carefully, because you could damage pretty bad the motherboard and kill it.

The themal paste is SUPER-IMPORTANT!!!!!!! You need to disassembly your macbook again and remove every remains of the old paste from the processor and from the heatsink, then apply new thermal paste, you can buy it online, here´s the link to buy it from ifixit

As you said, that´s an old laptop. So, the first thing you have to do is disassembly it. Because one of the possible problems could be a contaminated board, you need to do a deep maintenance. This is a youtube video of how tear-down your laptop: link You should use a paint brush (clean of course, we don´t want to make a piece of art with the motherboard ;)) ). And air can, or something to blow off the dust. While you are cleaning your laptop you should take a close look to the mainboard, and look for damaged areas and heat mark on the GPU. I also recommended to clean up the RAM memories. You could do that with an eraser (clean the golden contacts and make sure no remains of the eraser stays in the memories). When finish try your laptop and if it works, then you must change the dissipation paste in the CPU and the GPU, the GPU might have a dissipation rubber, you can get that online. If the problem persist leave a comment, so we could continue helping you.

I´ve seen this before, and the problem was a couple of damage capacitors. You need to disassembly your monitor and check the power supply, looking for anything out of the ordinary, like faulty capacitors (They usually looks swollen in the top). If you found this, check the voltage and micro-farads, look for others similar and make the change. The values in the voltage and micro-farads must never be under the original value.

Maybe you should try to download the windows ISO File and then make a fresh install of the Operative System, in order of correct all possible errors that your system might have. First: Make a Data Save of all your personal information in to a cloud or an external hard-drive. Second: Download ISO file from Microsoft server, here´s the Download Link Third: Make a boot-able USB drive with this tool: Download Link from Microsoft. This procedure should fix every errors contained in your currently Operative System, and then you should be able to update your system with the updates yet to come.

You need another computer, so you be able to download a windows ISO file, here is the Download Link for Windows 10 Then, with any utility you can make that iso boot-able from any USB drive, I use RUFUS app to do it. here is the Rufus download link

Need to try a DriverPack Solution Software and update the keyboard driver. If the problem persist your new keyboard might have a defect.