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Windows PC Errors

How to Fix ACPI_BIOS_ERROR BSOD (0x000000A5) on Windows

By ErrorFix · Updated October 27, 2026 · 8 min read

Error 0x000000A5Plain English: your BIOS handed Windows a set of power-management instructions Windows cannot read or trust — like a recipe written in a dialect the cook does not understand. Rather than guess and risk damaging hardware, Windows stopped the whole PC with a blue screen. The fix usually lives in the BIOS itself, not in Windows.
Quick answer: 0x000000A5 means the ACPI tables supplied by your BIOS are malformed or incompatible with your version of Windows. Update the BIOS firmware from your motherboard or laptop maker, reset the BIOS to its optimized defaults, turn off overclocking and aggressive memory profiles, then update your chipset drivers. Work the steps in order — most cases resolve by step 4.

What error 0x000000A5 means

ACPI stands for Advanced Configuration and Power Interface, and it is the language your motherboard's BIOS uses to tell Windows how the hardware is put together: which devices exist, how power states and sleep modes work, how fans and thermal zones behave, and how interrupts are routed. At boot, the BIOS hands Windows a set of data structures called ACPI tables — the DSDT and SSDT tables are the important ones — and Windows builds its entire picture of the machine from them.

When one of those tables is malformed, incomplete, or written to an older standard than Windows expects, Windows cannot build that picture safely. Rather than run on guesswork that could overheat a component or corrupt data, the kernel stops everything with the ACPI_BIOS_ERROR bug check, stop code 0x000000A5. Microsoft's bug check reference is blunt about where the blame sits: this is a BIOS problem first and a Windows problem second. That distinction matters, because it means the usual Windows repair toolbox — SFC, DISM, driver reinstalls — can only rule other things out. The actual fix is usually a newer BIOS, or undoing a BIOS setting that broke the tables.

That is also why 0x000000A5 so often appears right after a change: a Windows 10 to Windows 11 upgrade that enforces stricter ACPI rules, a BIOS update that introduced a regression, a new overclock, or a second-hand motherboard dropped into a build it was never certified for. If your blue screens started the day something changed, that change is your prime suspect.

Common causes

How to fix error 0x000000A5 — step by step

Work through these fixes in order, from the most likely cause to the least. Step 1 is the real fix in most cases, steps 2–4 clear the settings and driver problems that mimic it, step 5 rules out Windows-side lookalikes, and step 6 covers the boards that are genuinely incompatible.

  1. Update the BIOS firmware from the manufacturer. ACPI_BIOS_ERROR is most often a BIOS bug, so the real fix is a newer BIOS, not a Windows setting. Find your exact motherboard or laptop model on the maker's support site, download the latest BIOS, and follow that maker's update instructions precisely — usually from a USB drive inside the BIOS itself or through their Windows updater. Keep the PC on mains power and do not switch it off during the flash; an interrupted BIOS update can leave the board unbootable. After the update, boot normally and see whether the blue screen is gone before changing anything else.
  2. Reset the BIOS to its optimized defaults. Enter the BIOS setup (usually Delete or F2 during startup), choose Load Optimized Defaults or Restore Defaults, then Save and Exit. A hand-tweaked setting — a disabled ACPI feature, a changed APIC mode, or a power state the board handles badly — can make Windows reject the ACPI tables entirely, and resetting clears all of it at once. If the PC boots cleanly after the reset, reapply your own settings one at a time so you can spot the one that breaks it.
  3. Turn off overclocking and unstable memory profiles. In the BIOS, set the CPU back to stock speeds and disable XMP, EXPO, or any manual memory profile, then save and restart. Overclocked CPUs and memory running beyond their rated speeds can corrupt the data Windows reads from the BIOS at boot, including the ACPI tables, and the result is a 0x000000A5 crash that looks like a BIOS bug but is really unstable hardware settings. If the crashes stop at stock settings, your overclock was the trigger — re-tune it more conservatively or leave it off.
  4. Update chipset drivers and reinstall the ACPI driver. Download the latest chipset driver package from your motherboard or laptop maker (or from Intel or AMD directly for your chipset) and install it, then restart. Next, open Device Manager, expand System devices, right-click Microsoft ACPI-Compliant System, choose Uninstall device, and restart — Windows reinstalls a fresh ACPI driver on boot. A stale or mismatched chipset driver can misread the BIOS tables even when the BIOS itself is fine, and this step separates a driver problem from a BIOS problem.
  5. Repair Windows files and test your RAM. In an elevated Command Prompt, run DISM /Online /Cleanup-Image /RestoreHealth, then run sfc /scannow, and let both finish. Then search the Start menu for Windows Memory Diagnostic, choose Restart now and check for problems, and let it complete at least one full pass. Damaged system files and faulty RAM can both make Windows misread the ACPI tables at startup, so clearing them rules out two common lookalikes before you blame the motherboard.
  6. Check for a genuine BIOS incompatibility. If every step above has been tried and 0x000000A5 still appears on a clean boot, the BIOS itself may simply be incompatible with your version of Windows — this happens with very old boards upgraded to Windows 11 and with some budget boards whose ACPI tables were never fully compliant. Check the maker's site for a Windows 11 compatibility note or a newer BIOS beta, and contact their support with your board model and BIOS version. As a last resort, a clean Windows install on a supported configuration, or a board that the maker certifies for your Windows version, is the honest fix — no Windows setting can repair ACPI tables that are broken at the source.

Did this fix it? Quick checklist

If the blue screens continue after all six steps, note exactly when they happen — only at boot, only on wake from sleep, or only under load — and pass that detail to the board maker's support along with your BIOS version. Crashes tied to sleep and wake point at a specific ACPI power-state table, and makers sometimes ship a beta BIOS that fixes exactly that table. Keep your backups current while you wait: a board whose BIOS cannot describe its own hardware correctly is not a board to trust with unbacked-up data.

Frequently asked questions

What does ACPI_BIOS_ERROR (0x000000A5) mean?

It means Windows found a problem with the ACPI tables supplied by your BIOS — the data structures that describe how the motherboard manages power, fans, sleep states, and device configuration. If those tables are malformed, incomplete, or written for an older standard than Windows expects, Windows cannot build its power-management picture of the hardware and stops with the 0x000000A5 blue screen. Per Microsoft's bug check reference, this is a BIOS problem first and a Windows problem second, which is why updating the BIOS is usually the fix.

Can a Windows update cause ACPI_BIOS_ERROR?

Yes, in a specific way: a newer Windows version can enforce ACPI rules that an older BIOS never followed, so a PC that ran fine on Windows 10 can start blue-screening with 0x000000A5 after an upgrade to Windows 11. The BIOS did not change — Windows just started checking its tables more strictly. The fix is a BIOS update from the board maker that brings the tables up to the newer standard, or, if none exists, staying on the Windows version the board was certified for.

Is it safe to update the BIOS to fix 0x000000A5?

Yes, as long as you follow the maker's instructions exactly and never interrupt the flash. Download the BIOS only from the motherboard or laptop maker's own support site, confirm it matches your exact model, keep the PC plugged into mains power (and a laptop charged), and do not power off or restart until the update reports success. A BIOS flash that is cut short can brick the board, so never flash during a storm or on a battery that might die.

Will fixing 0x000000A5 delete my files?

No. Updating the BIOS, resetting BIOS defaults, disabling overclocking, updating chipset drivers, reinstalling the ACPI driver, and running DISM, SFC, and a memory test all leave your personal files untouched. Only the last-resort clean Windows install would touch your data, and even that can be done with a backup first. Still, back up anything important before a BIOS flash — not because the flash touches your files, but because any failed flash or failing board puts the whole PC at risk.

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