As promised, I returned with new information.
As I tried to boot from USB to update the BIOS, I was surprised that it will not boot from USB (even though it saw/recognized the USB memory).
I tried to install Windows 10 64bit on a spare hard drive and the same, it will not boot from USB. Pressed F8 at boot, selected the USB, but wasn't booting. So I started searching the internet for a solution. I found the solution myself poking trough BIOS settings: Advanced BIOS Features
-> Boot Sequence
-> First Boot Device [Removable]
-> Removable Device Priority
-> set USB-ZIP0
as first optionIntegrated Peripherals
-> USB Device Setting
-> lower you can see something like *** USB Storage Device Boot Setting ***
-> select your bootable USB stick
-> change value from FDD mode
to either Auto mode
or HDD mode
Saved settings, restarted and windows installation started without problems.
But ... while searching for this, I stumbled upon this thread: https://forum-de.msi.com/index.php?topic=97510.0
Translated to English and while I was scrolling down I saw this image with bios location on the motherboard:
On closer inspection my MS-7502 board had this written: W7502 IM710K. It's simple, it needed a IM7 bios and all this time I was trying to flash a MLN bios instead.
Searched the internet, found a vanilla W7502IM7.10R, flashed that from within Windows 10 Pro 64bit and everything is fine now. The chip is lowering itself to 2GHz at idle and jumps to 3GHz at full load (which is all I wanted).
I uploaded the BIOS I used along side the winflash used for flashing.
Backup BIOS first: Run Winflash (as administrator) -> Save as -> oldbios (or whatever you like).
To flash the BIOS: Run Start_Flash (as Administrator) -> select W7502IM7.10R file and flashing starts automatically, wait to finish flashing, then restart, enter bios, load defaults, save and that is all.
I also uploaded front panel jumpers pin configuration for those who need it (I know I did).
Hope this helps others. Thank you all for your support!