[URGENT]

Hello. The past few days have been so stressful for me because of my computer problems.

For starters, my computer is a 2015 HP ProDesk 400 G3 SFF. It has served me faultlessly for the past 5 years.

The problem started when my computer just randomly shut down whilst I was watching a film on my computer. Of course, it automatically restarted. But just a few seconds in, there suddenly was 3 red blinks and beeps, then 2 white ones on the power button. My screen kind of froze, as well, and my keyboard and mouse suddenly stopped working. I immediately unplugged the computer, and checked the PSU and CPU heatsink. The PSU was fine, and was just in normal temp. The CPU heatsink though, was burning hot. I grabbed a screwdriver, and removed the CPU fan and heatsink to check whatever happened. I then saw that the thermal paste was chapped dry. I wasn't quite alarmed as I thought it must have been natural, as the computer is already 5 years old. I also checked on HP's OFFICIAL support page what the blinks and beeps meant, and found out that it was an error code meant to help warn and troubleshoot computer problems. I found out that my error code 3.2 was signalling CPU overheat. Sp I was like, "AH well that confirms and settles it.". I thought all I had to do is re-apply thermal paste. So I ordered thermal paste online (we're on quarantine, can't go out). Took 3 days to arrive, and when it did, I immediately went on to work and re-paste my CPU.

After re-pasting I kinda let it settle in first for about 10 minutes before I decided to use the computer again. After using it, it then again overheated and the error code blinks were there again. So I was kinda taken ABACK and decided to check what the *censored* I did wrong.

I figured that I might have added too much paste. So, I cleaned off the newly applied paste, and re-pasted again. Now with just a pea-sized paste on the CPU, and 3 lines on the heatsink.

I then again let it settle first for a few minutes before turning the computer on. It WORKED fine, and there was no longer overheating issues. Within around 30 minutes of usage, it just suddenly shut down again. I was just bamboozled at that moment.

Like before, it automatically restarted. And yet again, with just a few seconds in, the blinks started again. This time it was 5 red blinks, and 2 white ones. I, again, checked it in the official HP support site, and saw that it was a "system board" error, particularly "The embedded controller cannot find valid firmware.".

The listed solutions are:

1. Remove any recently inserted Hardware.
2. Reset CMOS.
3. Update BIOS while removing AFFECTED components.
4. Test known good component.
5. Replace component or system board as needed.

So I started doing it. I turned off the computer, and unplugged the AC adapter/wire from the PSU. I removed the CMOS battery for about 30 minutes to let it reset. Then I turned the computer on. I went to the BIOS setup and found the BIOS update part. Clicked it. Downloaded the update. And just as I was about to reboot it after the update download, my computer just suddenly shut down. I tried it again and again, and really, it just shuts down right at that moment when I'm about to click the reboot button. It's like it doesn't want me to update it.

Guys, what should I do? How can I fix this? I really hope there is something I can do, and that it is nothing major as I don't exactly have the budget to make a major repair, let alone buy a new one. This is also pretty urgent as this is for my online schooling and some work. Thank you for taking the time to read this, and thanks in advance if your to help me with this problem!