Can adding RAM mess up the BIOS? A simple laptop upgrade that got complicated

An interesting service story today. Can swapping 4 GB RAM for 8 GB damage a laptop so that it can no longer even boot or install the operating system? I have personally found out that this is possible - here I will show what happened and present the solution to the problem. Does your laptop not boot after an upgrade attempt, does not see the USB drive with the system, does not boot the system even though it can see the drive? This is the topic for you.

The patient is a Lenovo B5400 laptop. On the one hand it's already quite old, several years old, still from the Windows 8 era, based on a dual-core Intel Pentium 3550M, but on the other hand it's well-preserved, with no scratches, a full set of hardware and a holding battery. It could still be suitable for social media, browsing the internet and making payments.
The only problem is that lukewarm SSHD drive and the measly 4 GB of RAM. Especially as that 4 GB is in the form of a single bone, and the replacement SSD I already have in stock from liquidation....

I started with this RAM. Something tempted me to try with two 8GB bones each. I guess that's silly, as RAM prices are knocking down, but everyone has different hobbies. I matched the two matching dice. Of course I disconnected the battery before running. With the 2x8 GB configuration the laptop wouldn't get up, and after running 4 + 8 GB there was an unusual problem. The laptop stopped booting Windows even though the drive was seen. I checked the standard stuff:
- second SATA media, second SATA port (I have a drive bay for the CD/DVD slot)
- booting from USB (Linux)
- bIOS settings, legacy, fastboot
- cMOS reset (battery)
Nothing wanted to work, so I decided to revert to the initial RAM configuration (the memory that came from the factory) and then I found that the problem still remains and booting does not work despite repeating the above described operations.

A quick web search quickly made me realise that I'm not the only one having this problem on this particular model of laptop:

It's exactly the same as mine! The laptop, colloquially speaking, has been "stoned" and now needs to be rescued. I decided on the "atomic" option, which is to upload a new BIOS with the CH341 programmer. This requires getting into the motherboard, i.e. you have to take the whole laptop apart.

The BIOS is in a tiny flash memory bone, here Winbond 25Q64FVSIG. the 64 in the name indicates the size - 64 megabits, or 8 megabytes. It needs to be programmed, but first also make a copy of it .

Such a memory is supposedly programmable on the chip, but in my experience this doesn't always work well, so I soldered the whole thing out with hot air and programmed it on a board-transfer from CH341. Of course the uploaded BIOS has to be preferably under the same version and revision of the motherboard as we have, plus it also contains the keys/OEM, so you either have to patch them yourself afterwards or resign yourself to losing them.... i was able to find a fit on the web for the upload candidate. Internet forums are a treasure mine though.

The laptop has started! The BIOS shows an older version. You can see the differences:

Windows from the old drive boots immediately, so it is however it was indeed the BIOS that was at fault:

However, the 8+8 version gives a blue screen of death, so in the end I opted for 8+4. 8+4 works in both combinations, so it's not like one of the new bones is faulty either.

The 4+8 version works fine. Also booting from USB now works. You can install your preferred operating system. There are not the problems that appeared before.

In summary , the standard procedure for adding RAM to the laptop ended with an unexpected problem. The BIOS had to be reloaded. In my case this went without too much trouble, but I realise that not every person adding a RAM die has the equipment and skills to solder, so it could be an unpleasant surprise for someone else. Anyway, even a quick web search shows that the same thing has happened to other people - and on the same laptop.
Now the laptop works and performs well as a station for browsing the internet, receiving emails and reading social media. It also does well with document editing and a printer.
The process shown worked, although I wouldn't say it was fully complete as I didn't patch the new BIOS, the ME region was also left unchanged, but I have a backup of the original batch in case I need to. I may try to address these issues in a separate topic. Here the laptop has passed the tests and is running stable.
Have you also already had such a "surprise" with the standard procedure for adding memory?