Fix FVE_E_NOT_SUPPORTED (0X80310015) BitLocker Error

Quick answer: Enable TPM in your BIOS/UEFI and make sure Secure Boot is on. If that doesn't work, run manage-bde -tpm and tpm.msc to verify TPM state, then check if the disk is using GPT partition table.

What's happening here

Error 0X80310015 means your system's hardware doesn't meet BitLocker's encryption requirements — specifically, Windows can't talk to a Trusted Platform Module (TPM) version 1.2 or higher. BitLocker relies on the TPM to store encryption keys securely, and if it's disabled, missing, or incompatible, the encryption wizard bails with this generic-sounding error.

You'll see this most often on: a custom-built PC where TPM is disabled by default in the BIOS, a laptop that shipped with Windows 10 Home (which lacks BitLocker device encryption support), or a system after a firmware update that reset BIOS settings to defaults. Windows 11 actually mandates TPM 2.0, so on those machines you'll hit this error if the TPM is off or the system is in Legacy BIOS mode instead of UEFI.

The fix steps

Try these in order. Step 1 fixes 80% of cases. Step 2 catches another 10%. Don't skip to step 3 unless you know your hardware is TPM-less.

Enable TPM in BIOS/UEFI
Reboot and enter your firmware settings (usually F2, Del, or F10 during startup). Look for a section labeled Security, Advanced, or Trusted Computing. The exact name varies by motherboard: on Dell it's "TPM 2.0 Security"; on Lenovo it's "Security Chip"; on ASUS it's "Intel Platform Trust Technology" or "AMD fTPM". Set it to Enabled. If you see an option for TPM State or Activation, set that to Enabled too. Save and exit.

The reason this works: BitLocker checks for TPM availability during the encryption wizard. If the TPM is present but disabled, Windows sees it as absent and throws 0X80310015. Enabling it in firmware makes the TPM visible to the OS again.
Switch from Legacy BIOS to UEFI (and enable Secure Boot)
In the same BIOS menu, find the Boot section and change Boot Mode from Legacy/CSM to UEFI. Then enable Secure Boot. Save and exit. If Windows was installed in Legacy mode, converting to UEFI requires the MBR2GPT tool — don't do it blindly. But if your system already has a fresh install of Windows 10 or 11, you're likely in UEFI already.

BitLocker requires UEFI and Secure Boot to work with TPM-based encryption. The reason is legacy BIOS doesn't support the measured boot process that TPM uses to verify boot components haven't been tampered with.
Check TPM status in Windows
Open Command Prompt as Administrator and run:
```
tpm.msc
```
This opens the TPM Management console. If you see "Compatible TPM cannot be found", the TPM is either disabled in BIOS (go back to step 1) or your CPU doesn't have one. If you see a version number (e.g., 2.0), it's working. Then run:
```
manage-bde -tpm
```
This shows TPM status and provisioning. If it says "TPM is not initialized", go to tpm.msc and under Actions, click "Prepare the TPM". Reboot.
Check disk partition style
Open Disk Management (diskmgmt.msc), right-click your system disk (usually Disk 0), and select Properties. Go to the Volumes tab. If Partition style says "Master Boot Record (MBR)", that's the problem. BitLocker requires GPT for system disks. Convert using the MBR2GPT tool:
```
mbr2gpt /convert /allowFullOS
```
This is safe on modern systems but back up data first. The conversion is non-destructive if it succeeds. Reboot and change BIOS to UEFI after.

When none of that works

If your motherboard genuinely lacks a TPM (very old hardware, or some budget mini PCs), you have two options:

Use a USB startup key instead of TPM — during BitLocker setup, choose "Require additional authentication at startup" and generate a startup key on a USB drive. This means you need the USB inserted every boot. It's less convenient but works.
Enable BitLocker without TPM via Group Policy — run gpedit.msc, go to Computer Configuration > Administrative Templates > Windows Components > BitLocker Drive Encryption > Operating System Drives. Enable "Require additional authentication at startup" and check "Allow BitLocker without a compatible TPM". This unlocks the option to skip TPM entirely. Apply, reboot, then try encrypting again.

Prevention for next time

Before installing Windows 10 or 11, go into your BIOS and enable TPM and Secure Boot first. Then use a GPT-formatted disk. If you're building a PC for someone else, buy a motherboard with a discrete TPM header (or a CPU with fTPM support, which is most Ryzen and Intel 8th-gen or newer). This saves you from chasing the 0X80310015 error later.

One last thing: if you're on a company-managed laptop, a corporate policy might block BitLocker setup. Check with your IT department before messing with BIOS settings — they might push a TPM enable policy remotely.