MSI produced 3 boards that are all known as MS-7366. The model numbers are P6NGM-L, P6NGM-FD, & P6NGM-FIH. Reflashing the Medion BIOS to the MSI BIOS version is risky so I hope you know what you're doing & are willing to accept the consequences if you botch the flash.
What you need to do is determine which MSI model number is the correct one for your board. I compared the specs between the 3 & it should be fairly easy. All you need to do is look at which video-out the board has:
P6NGM-L - VGA only
P6NGM-FD - 1 VGA, 1 DVI, no HDMI
P6NGM-FIH - 1 VGA, no DVI, 1 HDMI
Once you determine which board you have, here's where you can download the BIOS:
P6NGM-L product and bios page
P6NGM-FD product and bios page
P6NGM-FIH product and bios page
Once you download the file & unzip it, the BIOS file, flash utility & instructions on how to flash will all be in the folder. Hopefully you have a floppy drive. If not, I suggest you try using the "Live Update".
You're on your own from here....