Most of these faults trace back to software or heat, not a dead component. Below is an ordered, South African gaming checklist for the symptom in the heading, written so each step is something you can verify yourself before booking a repair or buying a replacement.
Quick Answer
Most of these faults trace back to software or heat, not a dead component. This usually comes down to drivers, a loose connector or background load rather than a faulty B850 motherboard. Run a fixed 20-minute test after each change and keep the one that holds at a steady frame rate or a stable temperature under 85C.
Drivers, BIOS and Windows
Check that a recent Windows feature update did not swap your tuned driver for a generic Microsoft one overnight. Roll the GPU driver back to the last stable release, then do a clean reinstall using DDU so leftover files do not clash.
PSU and connector checks
Re-seat the 12V-2x6 and 8-pin EPS connectors fully; a half-clicked plug shows up as random shutdowns under load. Verify the PSU wattage matches the load; a high-end card wants real headroom, so a 1000W unit is a sensible floor for top builds.
Heat and airflow checks
Reseat the cooler and apply a fresh pea of paste if temps spiked after a recent strip-down. Confirm the case has a clear front-to-back path and that no cable is resting against a 120mm or 140mm fan.
FAQ
How long should each test run?
Use a fixed 20-minute load that reliably triggers the fault. A shorter burst can hide a thermal or memory problem that only appears once the system is fully warmed up at 80C or higher.
How do I know it is not the GPU driver?
Run DDU in safe mode and install one clean driver. If the symptom vanishes you found it; if it returns, move on to heat, power and memory checks.
Is it safe to keep using the PC like this?
If it shuts down or blue-screens, stop heavy loads until you find the cause. Repeated hard crashes can corrupt the boot drive, so back up your data before deep testing.
Confirm the part before you buy
Once the checklist points at a single component, browse the matching B850 motherboards on Evetech and replace only what failed the tests.