Microsoft Teams won’t launch even after full system rebuild and updates

Use the Teams client health guidance and the new Teams launch troubleshooting steps to further diagnose and fix the launch failure.

1. Check Teams client health insight

• In the Teams client health dashboard, look for this device/user under Launch failure and review the Insight column.
• If the insight is:
  • Unable to navigate to Teams endpoint or Timed out waiting for Teams endpoint: Review firewall/proxy configuration and ensure all Teams endpoints are reachable and not blocked.
  • Teams application contains a script error: Sign out of Teams and sign back in.
  • Unsupported OS version: Update Windows to a supported version per Teams client system requirements.

2. Run the TeamsLaunchCheck.ps1 script (new Teams)

• Use the TeamsLaunchCheck.ps1 PowerShell script described in the “Resolve issues when starting the new Teams app” article. This script automates all diagnostic checks required to identify why new Teams fails to start.
• If the script is not available, perform the manual checks below.

3. Verify Cookies and Cache shell folders are not reparse points

• Run in PowerShell:

    (gp ([environment]::getfolderpath("Cookies"))).Attributes -match 'ReparsePoint'
    (gp ([environment]::getfolderpath("InternetCache"))).Attributes -match 'ReparsePoint'
  

• If either returns True, open Registry Editor and go to: Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
• For the affected entry, reset to a non–reparse point path, for example:
  • Cookies → %USERPROFILE%\AppData\Local\Microsoft\Windows\INetCookies
  • Cache → %USERPROFILE%\AppData\Local\Microsoft\Windows\INetCache

4. Verify TEMP and TMP are not reparse points

• Run in PowerShell:

    gci env:* | ?{@("TEMP", "TMP").Contains($_.Name)} | %{$_.Value+" - "+((gp $_.Value).Attributes -match 'ReparsePoint')}
  

• If any result shows True, change the TEMP/TMP environment variable values to a folder path that is not a reparse point.

5. Check AppData folder permissions and structure

• Ensure Read permission exists for all required AppData paths. Use Test-Path to verify access, for example:

    Test-Path -Path $env:USERPROFILE\AppData\Local
  

• Repeat for all directories listed in the resolution (Local, Local\Microsoft, Local\Microsoft\Windows, INetCache, INetCookies, WindowsApps, Packages, Temp, LocalLow, Roaming, etc.).
• If Test-Path fails due to permissions, have an administrator grant Read permission for the user and Full control for SYSTEM and Administrators on these directories.

6. Remove invalid files that shadow system folders

• For each directory listed in the resolution, run:

    Test-Path -Path <full path> -PathType Leaf
  

• If this returns True, a file exists where a folder is required (for example, a file named Libraries where %AppData%\Microsoft\Windows\Libraries should be a folder).
• Delete the file and recreate the folder with the same full path.

7. Check SYSTEM and Administrators permissions

• For each directory from step 5, verify that the SYSTEM account and Administrators group have Full control. If not, have an administrator adjust ACLs accordingly.

8. Verify SYSAPPID permission on Teams installation

• Run in PowerShell:

    Get-AppxPackage MSTeams | %{$_.InstallLocation+" - "+(((Get-Acl $_.InstallLocation).sddl -split "\(" | ?{$_ -match "WIN:/\/\SYSAPPID"} | Measure).count -eq 1)}
  

• Ensure the result indicates the SYSAPPID permission is present (returns True). If not, adjust permissions or reinstall Teams so that the correct appx permissions are applied.

9. Check AllowAllTrustedApps policy and Windows build

• Run winver and compare the OS build with:
  • Windows 11: 21H2 build 22000.2777, 22H2 build 22621.2506
  • Windows 10: 21H2 build 19044.4046, 22H2 build 19045.3636
• If the build is earlier than these and Teams still won’t start, check the AllowAllTrustedApps policy:
  • In Registry Editor, check AllowAllTrustedApps under:
    • Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock
    • or Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Appx
  • If the value is 0, set it to 1, then try starting Teams again.
• Alternatively, update Windows to at least Windows 11 version 22H2 OS build 22621.2506 or later so new Teams can start without enabling this policy.

10. If profile corruption is suspected

• If the manual checks show no issues but Teams still won’t launch, have a local administrator delete the user profile on the machine as described in the resolution, then sign in again to recreate the profile and reinstall Teams.

11. If the issue persists

• After completing these checks, if Teams still appears only as a background process and never shows a window, use the Teams client health dashboard insight plus these diagnostics and contact Microsoft Support for further investigation.

References:

• Resolve Teams client launch failures
• Resolve issues when starting the new Teams app
• Teams starts with a white screen
• Latest Teams Desktop Version getting auto restart, very strange issue. teams not working completely for desktop version. - Microsoft Q&A
• Microsoft Teams opening issue. - Microsoft Q&A
• Teams keeps crashing and restarting after updating to version 25332.1210.4188.1171 - Microsoft Q&A
• Unable to access teams meetings - app just hangs when joining meeting - Microsoft Q&A
• Teams needs Edge WebView2 to be installed but installation fails, saying that the Runtime is already installed. - Microsoft Q&A