As a Computer Repair Expert, many times when I work on computers and find problems with Windows Defender, there are a number of factors contributing to these issues which may include malware infection, software conflicts (possibly with another antivirus program), corrupted registry, etc.
One Particular problems is When Windows Defender does not start automatically when Windows starts and when Windows Defender is started manually via Action Center it may display an error code or just turn off after a few seconds.
When you encounter these problems, here are some things you can try:
1. Restart your PC
Many times the issue is resolved by simple restart.
2. Remove existing antivirus and antispyware software
If your PC still has another antivirus installed or if one was installed previously then you should use appropriate removal tool to remove all third party antivirus and antispyware programs.
3. Scan your PC for Malware
4. Time to hire a pro to help! I’m available or you can hire a local technician.
There are more steps your can find on the following link below. However, if the above actions don’t work, I recommend having a trained professional look at it.