A320M-HDV R4.0 Ryzen 3400g freezing

The A320M-HDV is a very basic, ultra budget board. Given the symptoms I would
guess the VRMs are getting too hot when you are running games for prolonged periods.
There are no heatsinks on the VRMs of that board so they rely exclusively on airflow
over the VRM area. Try positioning a fan over the VRM section, even pointing a desk
fan at the side of your PC with the side panel removed will work for testing.

There is always an element of risk any time you update the BIOS, up or down though
downgrading is inherently more risky. In your case however, you should be able
to downgrade as there is no generational support added from 3.3 to 3.7. It IS
risky to downgrade and it can kill your board. If you choose to go this route
then do the following to minimize risk:

1. Clear CMOS (Check your user manual if you don't know how to do this)
2. Power on the system after the clear and allow it to boot into windows then
shut down. This will ensure defaults are loaded. Do not change anything in the BIOS.
3. Download the "Instant Flash" 3.30 BIOS version from your product page (be sure
it's for the R4.0 board) and extract it onto a FAT32 fromatted USB flash drive.
4. Go into the BIOS and load system defaults (just to be extra careful) and reboot.
5. Reenter the BIOS and use the instant flash utility with your flash drive
containing the BIOS update inserted in one of the rear USB ports. It should
detect the BIOS version and ask if you want to update to it.
6. DO NOT POWER OFF THE SYSTEM, even if it looks like it turned off and won't
come back on. Let it run for at least 20 mins (if it won't show anything on the
screen).

The system should complete the update and automatically restart. All being well
you will boot into windows and should be running version 3.30. After it has booted
into the OS you can now feel free to restart and change whatever BIOS settings
you need to (enable XMP etc).

I say this again, do this at your own risk. I would try the fan test first.

Thanks for the link. In that case I am sure ASRock is aware of the issue (through
support tickets).

If you have upgraded to 4.0 I would not recommend downgrading to 3.3 now. I typically
avoid downgrading whenever there is a version number difference, 4 down to 3 in
this instance. In many cases it bricks the board. Within the same version number,
provided new CPU support has not been added, is usually fine. Whenever new CPU
support is added the same rule applies as with version numbers. Usually new CPU
support is accompanied by a version number change however.

Thanks for the follow up GGGM, here's hoping your kids get enjoyment from the system
for a good long time