When you boot your system, Windows Defender attempts to start but then fails with the error message:

Application failed to initialise: 0x800106ba. A problem caused Windows Defender Service to stop. To start the service, restart your computer or search Help and Support for how to start a service manually.

There are a number of possible solutions, so try them in the following order:

1. Re-install Windows Defender: download the latest version here http://tinyurl.com/85qsa (click on Download Latest Version). Ensure that you memorise the location of the downloaded file, and after the download has completed, use Windows Explorer to navigate to the file WindowsDefender.msi and right-click on it to choose Install.

   To access Windows Explorer quickly, press and hold the Windows Logo key (to the left of the space bar with the icon) and then press the letter E - release both.

   Note: a complete list of Windows Keyboard Shortcuts is here: http://tinyurl.com/psrkk

2. Go to Start | Control Panel | Administrative Tools | Services and scroll down to Windows Defender. If it the Status is not "Started" and the Startup Type is not "Automatic" right-click and select Properties and on the General tab, change the Startup Type to "Automatic" and then click Start. Then re-boot the computer.

3. Check that Client for Microsoft Networks is installed: click on Start | My Network Places and select Properties; this should display icons for devices or functions that allow you to connect to the internet.  These could include Local Area Connection or your broadband USB modem (e.g. Speedtouch Connection, BT Voyager 105, etc.). Whichever is relevant to your particular method of connection, right-click on the item and select Properties.

   If Client for Microsoft Networks is not shown,  click the "Install..." button to begin the process of installing this component. Select "Client" as the type of component from the list in the new window that appears. Click the "Add..." button to continue. Choose "Microsoft" from the list of manufacturers shown on the left of the active window. Then choose "Client for Microsoft Windows" from the list of Network Clients on the right side of the window. Click the "OK" button to continue. Complete the installation by clicking the "OK" button to close the window, then proceed to reboot the computer.

4. Go to Start | Control Panel | Add/Remove Programs | Windows Defender and select Change. Then click on Next | Update | Install and when it has completed, leave the box ticked to Check for Updates .... (please ensure that your internet connection is live). Then re-boot the computer.

5. If all these attempts fail, please let me know by email.