Windows defender program is one of the most amazing programs given by Microsoft in the Windows 10 version. It is a sort of antivirus that is able to scan the whole computer to find out the virus and other infections. When you launch the Windows defender in the computer, you may get Windows defender error 0x80501105 sometimes. It is really a very critical error issue that comes to you due to deletion of some important files associated with this program. You need to go through the manual or automatic error fixing methods to fix the issue. For automatic troubleshooting, you should download and install Advanced System Repair tool in the computer.