ACPI_BIOS_ERROR 0x000000A5 and HAL_INITIALIZATION_FAILED 0x0000005C

Fix it now

0x000000A5 means the ACPI BIOS is not fully compliant with the ACPI specification, and Microsoft’s published resolution is short: obtain a new BIOS from the vendor. Parameter 1 says which incompatibility was found, and several of its values point at firmware tables rather than at anything you can change in setup.

msinfo32

1. Note the current firmware version from System Information, or from the setup screen on a machine that will not start.
2. Get parameter 1 from the BugCheck event in the System log or from the dump. 0x11 means the system could not enter ACPI mode; 0x10009 means the Fixed ACPI Description Table could not be located; 0x1000A means the Root System Description Pointer or Extended System Description Table could not be located.
3. Flash the current firmware from the machine or board vendor’s own support page for that exact model. This is the documented resolution, not a last resort.
4. If the firmware was recently reset or the machine has sat unpowered for a long time, load setup defaults, set the date and time, and check every storage and power option before booting.
5. If the code is 0x000000E0 rather than 0x000000A5, stop and go to the hardware vendor – see the note below.

0x000000E0 is not a firmware setting problem. Microsoft states plainly that the BIOS has reported a component so faulty that Windows cannot operate, that the parameters are issued by the BIOS and can only be interpreted by the hardware vendor, and that Microsoft cannot address the error.

If the machine starts on current firmware at defaults, stop here. The next section covers what each code in this group actually reports.

Why it happens

ACPI is the contract between firmware and operating system covering power states, device enumeration, interrupt routing and thermal management. The firmware publishes a set of tables describing the platform, and Windows reads them during startup. If those tables are missing, malformed or describe something Windows cannot work with, there is no recovery – the operating system has no other way to find out what the machine is.

0x000000A5 is that rejection, and parameter 1 is the only thing that turns it into a specific action. 0x01 means ACPI could not find the System Control Interrupt vector in the resources handed to it. 0x02 means the ACPI BIOS could not process the resource list for the PCI root buses. 0x03 means a control method failed while device extensions were being created. 0x0D means a required method or object was missing from the namespace. 0x11 means the system could not enter ACPI mode. 0x10009 means the Fixed ACPI Description Table could not be located, and 0x1000A the Root System Description Pointer or Extended System Description Table.

Microsoft’s resolution is unusually direct for a bug check: if you are not debugging, this error indicates that you have to obtain a new BIOS. There is a published fallback – turning ACPI mode off by pressing F7 when text-mode setup prompts for storage drivers – but that belongs to an installer that current Windows does not have, so on a modern machine the firmware update is the answer rather than the first option.

The rest of the group is thinner than it looks. 0x0000005C says the hardware abstraction layer initialisation failed, and nothing else – no parameters, no cause, no resolution. 0x00000031 says system initialisation failed at a very early stage, with no parameters, and Microsoft states a debugger is required to analyse it. 0x00000079 does have a real parameter table and a specific cause: the HAL revision level or configuration does not match the kernel or the computer, most often because someone manually updated Ntoskrnl.exe or Hal.dll, or because a multiprocessor HAL has ended up paired with a single-processor kernel.

Full reference

0x000000A5 parameter 1, the values you are likely to see

What each code in this group actually publishes

0x00000079 in more detail

MISMATCHED_HAL is one of the few codes in this family with a fully published parameter table. Parameter 1 of 0x1 gives the major processor control block level of Ntoskrnl.exe in parameter 2 and of Hal.dll in parameter 3, so the mismatch is visible directly. Parameter 1 of 0x2 gives the build types of the same two files. Parameter 1 of 0x3 gives the size and version of the loader parameter extension, meaning the loader and the HAL disagree. Microsoft’s cause note is that this often happens when someone manually updates one of those two files, and that a machine can end up with a multiprocessor HAL and a single-processor kernel or the reverse.

Where firmware updates go wrong

1. Record the current version first. Some vendors do not publish older packages, and a rollback may not be possible.
2. Use the vendor’s own tool for that exact model. Firmware from a similar model is not interchangeable.
3. Run it on mains power, with the battery fitted on a laptop, and do not interrupt it.
4. Load setup defaults afterwards, then reapply the settings the machine needs – storage mode above all.
5. Set the date and time before booting Windows. A wrong clock produces its own set of problems that will look unrelated.

When the machine will not start at all

• Check whether the disk is detected in firmware setup. If it is not, this is a different problem from an ACPI rejection.
• Boot the recovery environment and try System Restore, which undoes a driver or update change without touching firmware.
• Where the firmware update itself failed, most boards have a recovery mode – a specific key combination or a file on a USB stick – documented by the vendor.
• Remove add-in cards and non-essential devices and try again with the minimum viable configuration.
• If the code is 0x00000031 or 0x0000005C, there is very little published to work from, so treat the dump and a vendor case as the route rather than trial and error.

Every code this article covers

Confirm the fix worked

1. System Information reports the firmware version you intended to install.
2. The machine completes three cold starts without a stop code.
3. Device Manager shows no devices with an exclamation point, particularly under System devices.
4. Sleep and resume work, which exercises the ACPI path that was rejected.
5. The clock holds its time across a full power-off, if a flat coin cell was part of the story.

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