One of my friend bough dell laptop recently which was running windows 8.1 that came pre-installed on this machine. However when he tried to upgrade it to windows 10, it stopped at 99% no matter how long he waited it to complete. so this is how we fixed this issue

windows 10 upgrade assistant stuck at 99

Solution

• Uninstall Antivirus program (very important)
• Restart your computer
• Press Windows + R key , it will open run command window and there type ” services.msc “, as shown in image below.

run services.msc

• On next screen it will show you a long list on services, you need to find windows update service. as shown in image below.

Windows update service

• Right click on it and select properties then from drop down menu select disabled and apply. as shown in image below.

Windows update service disabled

• Now start windows upgrade assistant and it should complete installation without any errors