What was the old system - uefi?
What has windows on it the hdd or the ssd?
Is the bios set to boot from the drive that has windows on it?
You can always test if it will boot from either a windows creation usb
or a linux usb.
Have you read the troubleshooting guide at the top of the hardware forum.
Hardware | Tech Support Guy (techguy.org)

 

Not really sure about the old system, the last motherboard swap was performed in like 2014 or so and the current system is set to uefi by default.
Windows is on a ssd, but when I check the ssd status in the bios it says "not support" and it's greyed out. Could be the problem.
The only option concerning the data storage is titled "uefi hard disk" and has a boot priority. No mention of ssd whatsoever.

 

if changing it would affect the hdd data in any way

First and foremost, IF you value this data, you make multiple backups. I have a saying "Data you do not have at the very least two copies is data you do not care about"

Next, does the system complete POST? Are you able to enter the bios?

It would REALLY help if you posted ALL of your exact system specs. You are posting in a hardware forum and no one has any idea what hardware you are running with the exception of some msi motherboard. Note exact means just that; brand and model# for ALL of your components.

You do understand that unless you follow the procedure outlined at the top of the hw forum for swapping motherboards without a clean install, there is a good chance the system will not boot.

 

There is a subtle flash of MSI logo right after startup saying "Press del to run bios setup or f11 to run boot menu" below that it says "ctrl+f5 to activate m-flash for bios update". This text just flashes (not even a second) and then it goes into blackscreen for a while and msi click bios 5 screen pops up afterwards. System doesn't even show POST, just what I described.
Specs are:
CPU: Intel core i5-12400f lga1700 with arctic ii 240 water cooler
MB: Msi Z690-a ddr4
RAM: Kingston fury 8gb ddr4 3200 mHz cl16 beast
GPU: Nvidia geforce gtx 1660-ti
SSD (with win10): Kingston sv300 (120gb)
HDD: St500dm002-1bd (500gb),
Wdc wd4004fzwx (4tb)
PSU: Fsp raider ra 750 W

 

Follow the guide at the top of the forum for problem builds. Get the system to POST first with no drives connected. If you are successful, then reassemble the system with a single drive and clean install windows.

Just an observation. Your pw supply is pretty old. I think those stopped production in around 2015 or so. Personally, I use a pw supply for 5~7yr max then replace it.

 

Solved, all that needed to be done was to change the bios boot type from uefi to csm, as the system is older an was originally booted with csm.

 

Great work
Thanks for posting your fix