Fix 0x0000007B INACCESSIBLE_BOOT_DEVICE

Quick answer: Boot into Safe Mode, then change the SATA controller mode in BIOS from IDE to AHCI (or vice versa), or reinstall the storage driver.

That blue screen with 0x0000007B is a pain, but it's almost always about Windows losing its grip on your hard drive or SSD. The system can't find the boot device because the storage controller driver is missing, wrong, or mismatched with the BIOS setting. I've seen this on older machines after a Windows update, and on newer ones when someone digs into the BIOS and flips SATA mode without thinking. Last month I had a client whose Windows 10 box refused to boot after a routine Dell driver update — the update swapped the storage driver and the BIOS was set to RAID.

Why This Happens

Windows loads a driver to talk to your disk controller. If that driver doesn't match the controller mode (IDE, AHCI, RAID/NVMe), the system can't read the boot files. This usually happens after a BIOS change, a disk cloning job, or a Windows feature update that overwrites the driver. The error can also pop up if the boot configuration data (BCD) is corrupt, but that's less common.

Fix Steps

Try Safe Mode first. Restart your PC, and when the spinner appears, hold the power button to force shutdown. Do this 3 times. On the third restart, Windows should show the recovery screen. Go to Troubleshoot → Advanced options → Startup Settings → Restart. Choose Safe Mode (option 4). If it boots to Safe Mode, the problem is likely the driver — you can fix it from there.
If Safe Mode works, change the SATA mode in BIOS. Restart, press F2/F10/Del (depends on your motherboard) to enter BIOS. Look for Storage, SATA Configuration, or Drive Controller. Change the mode from IDE to AHCI (or vice versa). Save and exit. Windows may boot now because the driver that loaded in Safe Mode is a generic one that works with both.
If that doesn't fix it, reinstall the storage driver. While in Safe Mode, open Device Manager (devmgmt.msc). Expand IDE ATA/ATAPI controllers or Storage controllers. Right-click the controller (e.g., Intel SATA AHCI Controller) and choose Uninstall device. Check Delete the driver software for this device, then restart. Windows will reinstall a default driver on boot. If you're using an NVMe SSD, look under Storage controllers for something like Standard NVM Express Controller.
Use Command Prompt to force AHCI. If you can't get into Safe Mode, boot from a Windows installation USB. Pick Repair your computer → Troubleshoot → Command Prompt. Type regedit and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\storahci. Set the Start value to 0 (that's the AHCI driver). Also check storeahci if it exists. Then exit and restart — this forces Windows to enable AHCI at boot.
Check for BIOS update. If the above fails, your motherboard might have a buggy SATA implementation. Check the manufacturer's site for a BIOS update. I had a client with an ASUS Prime board and a 10th-gen Intel chip that BSOD'd on every cold boot until we updated the BIOS — that solved it.

Alternative Fixes

Run Startup Repair. Boot from Windows USB, go to Troubleshoot → Advanced options → Startup Repair. It sometimes fixes BCD issues that mimic this error.
Check your disk connections. If it's a desktop, power off and reseat the SATA cable or NVMe drive. A loose connection can cause this error randomly.
Revert recent changes. Did you just clone your HDD to an SSD? The clone might have missed the boot partition. Use a tool like Macrium Reflect to redo it with the right cloning mode.

Prevention Tip

Before you ever touch the BIOS or clone a disk, set the storage mode to AHCI in BIOS, then install Windows fresh. That's the cleanest path. If you're already on AHCI, leave it alone. And if you're updating storage drivers, use the manufacturer's tool (Intel Driver & Support Assistant, Dell Command Update) rather than random driver updaters — I've seen those break more than they fix.