CPU Problems: No Boot, Shutdowns, High Temperature, Low Performance
CPUs rarely fail. Most CPU-looking symptoms come from power cables, BIOS version, or cooler mounting. Work through these in order.
Fans spin but no display
If fans spin but nothing appears, the CPU may not be running or not recognised by the board.
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- Check the CPU power connector (8-pin, sometimes 8+4). Forgetting it while the 24-pin is connected is very common.→ If it was missing, simply connecting it fixes the boot.
- Check the board's diagnostic LEDs. A stuck CPU LED means it halts at the CPU stage.
- Verify the BIOS version supports your CPU. Newer CPUs will not boot on older BIOS.→ If unsupported, use BIOS Flashback or borrow an older CPU to update.
- Check for over-tightening. Tighten diagonally and evenly; uneven pressure causes poor contact.
- Remove the CPU and inspect for bent pins (board side on LGA, CPU side on AM4).Tool: Bright light; a magnifier helps→ A bent pin is the cause. Forcing it straight often breaks it.
Shuts down or reboots under load
Crashes only under load usually point to power delivery or cooling, not the CPU itself.
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- Log CPU temperature just before the crash. Near 95°C points to cooling; a low temperature points to power.Tool: A monitoring tool such as HWiNFO
- Temporarily lower the power limits (PL1/PL2, or disable PBO). If it stops crashing, power or cooling is short.
- Check PSU capacity and age. Units over five years old can fail under load even at adequate wattage.
- Disable XMP/EXPO and retest. Memory instability is often mistaken for a CPU fault.
Runs hot, hits 90°C quickly
Modern CPUs throttle rather than fail. But throttling costs performance, so cooling is a performance question.
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- Confirm the protective film on the cooler base was removed. Forgetting it is not rare.
- Remove the cooler and look at the paste spread. Contact only in the centre or on one side means uneven pressure.→ Reapply and retighten diagonally and evenly.
- Check case airflow: intake at the front, exhaust at the rear and top. Without front intake, a better cooler will not help.
- For an AIO, ensure the radiator sits higher than the pump. A pump at the highest point traps air and stops working properly.