When This Error Hits
You're working on a Dell Latitude 5490 or an HP EliteBook 840 G6. Everything's fine until you close the lid for lunch. Come back, hit the power button, and instead of your desktop, you get a blue screen with ERROR_ACPI_ERROR (0x0000029D). The system reboots, maybe posts, but the second Windows tries to restore power states – boom, crash. I've seen this most often after a Windows Update that changed the power scheme without telling you, or after a firmware update that didn't fully apply.
Root Cause – Plain English
ACPI is the layer between Windows and your motherboard's power management. It tells Windows what voltage your CPU needs, how deep the sleep states go, and when fans spin. The 0x0000029D error means Windows tried to read a power state table from the BIOS, but the table was garbled. Could be a corrupted CMOS, a bad firmware patch, or a driver that wrote junk into the ACPI namespace.
The culprit here is almost always one of three things: fast startup (which caches power state info improperly), stale BIOS settings that don't match what Windows expects, or chipset drivers that got borked by an update. Don't bother reinstalling Windows – that's overkill 90% of the time.
The Fix – Step by Step
- Clear CMOS and reset BIOS to defaults. Power off, unplug the AC adapter, remove the CMOS battery for 30 seconds (or use the jumper if your board has one). Reassemble and boot into BIOS (F2, F10, Del – depends on your brand). Load 'Optimized Defaults', save and exit. This wipes any corrupted power tables.
- Disable Fast Startup in Windows. Open Control Panel → Power Options → Choose what the power buttons do → Change settings that are currently unavailable. Uncheck 'Turn on fast startup (recommended)'. Click Save changes. This forces a full shutdown every time – no cached state to corrupt.
- Update chipset drivers from the OEM, not Windows Update. Go to Dell/HP/Lenovo support site, download the latest chipset driver for your exact model. Uninstall the current one in Device Manager (System Devices → right-click each chipset component → Uninstall device, check 'Delete driver software'). Reboot and install fresh. Windows Update often delivers generic drivers that miss vendor-specific ACPI tables.
- Run the System File Checker. Open Command Prompt as admin, type
sfc /scannow. Let it fix any corrupted system files. This catches cases where Windows power policy files themselves are bad. - Repair the ACPI driver manually. In Device Manager, expand System devices. Right-click 'Microsoft ACPI-Compliant System' → Update driver → Browse my computer → Let me pick from a list → Select 'Microsoft ACPI-Compliant System' (the default). If it's already selected, choose 'ACPI Fixed Feature Button' instead, then switch back. This forces a re-register of the ACPI interfaces.
If It Still Fails
Three things left to check. First, open Event Viewer → Windows Logs → System, filter by source 'ACPI' or 'Kernel-Power'. You'll often see event ID 41 or 157 – that points to a specific faulty ACPI table. Google that table name (like 'FACP' or 'DSDT') with your motherboard model.
Second, try a clean boot. Run msconfig, select Selective startup, uncheck 'Load startup items'. If the error stops, you've got a third-party driver or service corrupting the ACPI namespace. Narrow it down by re-enabling half at a time.
Third and last – update the BIOS itself. I've seen machines where the OEM shipping BIOS had a bug in the S3 sleep state table, and a later firmware revision fixed it. Download from the manufacturer's site, run the update from a USB stick (not from within Windows – you don't want the flash tool to trigger the same ACPI bug).
If none of that works, you're looking at a hardware fault – bad CMOS battery, failing EC (embedded controller) chip, or a motherboard trace that's gone flaky. That's a repair shop job, not something you fix with software.