That board shows support for the 3700x since the first BIOS version, 7C37v11, so I don't see that being possible. Besides which, any motherboard bought recently would undoubtedly have a much newer BIOS than the original one already installed anyhow since over the course of the last year ALL these motherboards were entirely out of stock meaning anything bought now would not be a sample that was manufactured early on.
Anything is possible, but you'd have to have either bought the board the first couple of weeks after it was originally released OR live in a market where product doesn't move very fast so you ended up with an old stock sample from somebody's back shelf OR are the unluckiest person in the world and ordered through a major manufacturer who just happened to have found "one more" behind a pallet in the back of the warehouse that had been sitting there unnoticed throughout the last 12 to 15 months.
It's unfortunate that this board does not have BIOS flashback, so you'll have to do as you said and either buy a cheap APU, or take it to somewhere like Microcenter or Best Buy that will upgrade the bios for you for cheap (Usually 10-15 bucks) or contact AMD to get one of the loaner CPU kits, or else send it to MSI to be flashed.
I'm pretty skeptical that's the issue though, but again, never rule anything out until you know for sure. I personally have not seen ANY X570 motherboard not work with ANY of the Ryzen 3000 series CPUs. At least not to the extent that they wouldn't even allow you to POST.
Are we 200% certain that the CPU was correctly installed and no pins were bent during the installation? Have we checked to see that it the monitor is set to the input type of which is in use, being HDMI, DP, etc.? Tried a different input type? I've seen a lot of systems that for whatever reason did not want to use HDMI at first, or visa versa, with DP. If your monitor supports a different display type than whatever you are using now, try that, can't hurt.
I'd also TRIPLE check ALL of the noted check points here:
"No POST", "system won't boot", and "no video output" troubleshooting checklist This checklist is a compilation of troubleshooting ideas from many forum members. It's very important to actually perform every step in the checklist if you want to effectively troubleshoot your problem. 1.Did you...
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