Fixing Boot

Hi everyone.
Thank you for having me.

I have recently started using a new laptop (HP Pavilion 15 cs, Windows 10 home 1909) and had many work tools installed on it.
Yesterday I tried to install a new RAM which matches the older one, increasing from 8 to 16gb.
After putting everything back together, I received an error message saying boot device isn't found. At first I was sure I damaged the MoBo or touched the NVME the OS is installed on, but it does appear in the BIOS and the memory was installed properly.
It was suggested by a friend who is a computer technician that an update stopped at the middle caused the damage.

Since yesterday I was attempting to fix the boot via various methods:
I tried to make a repair from the windows menu, but after diagnostics there was no positive results. I've tried a DOK with Windows installation on it, but wasn't able to repair it.
I also found an old post regarding the subject, trying to bootrec /FixBoot and after many times of getting "access in denied", I managed to solve it (bootsect/nt60 sys), but still no results.

What I wasn't able to do via diskpart is set the volume to Active, since I receive an error:
The selected disk is not a fixed MBR disk.
The ACTIVE command can only be used on fixed MBR disks.

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I will be glad not being needed to reinstall everything again. Therefor will happily accept help and support.
Either via Windows tools or external tools (someone suggested HBCD).

Please help with anything you think is relevant.

Thank you

sounds like your hard drive is GPT, check the settings in your BIOS and see if it is set as UEFI and not legacy. Changing the RAM definetely shouldn´t have caused damage to the boot loader.

You need to know type of file system as you can't fix MBR if it doesn't have one

xaccell said:

sounds like your hard drive is GPT, check the settings in your BIOS and see if it is set as UEFI and not legacy. Changing the RAM definetely shouldn´t have caused damage to the boot loader.

To be honest, I'm not sure how it is configured. Adding a photo

AndreTen said:

Try to disable (temporary) Secure boot

Thank you.
Just tried it. Getting blue screen with "inaccessible boot device"

AndreTen said:

Is hard drive visible inside BIOS (or UEFI) ?

Yes. And in diskpart i can see the different volumes including hidden partitions.

before going into more complex things, try the old chkdsk

xaccell said:

before going into more complex things, try the old chkdsk

One of the first things I was asked to do.
It returned with 0 errors, but does it necessarily mean it is true?