Windows Defender Won’t Start – How to Avoid This Problem

Why won’t Windows Defender start when I start my computer

The problem is basically that we turn on a Windows computer and see that the antivirus does not start. It’s installed, we haven’t touched anything apparently, but it’s not actually protecting us. It’s like it’s locked.

Why is this happening? The causes are diverse and there is no single reason. The normal thing is that it is due to a software conflict. Some program that interferes and causes Windows Defender to not start correctly on the computer. For example, if we have installed something recently or if we have another antivirus that causes a conflict.

It could also happen that the reason is a incomplete update. This is relatively common and happens with many programs or services in the operating system. If we have updated Windows but for some reason that update has not been completed correctly, it can lead to failures of this type. In this case it could affect Microsoft’s antivirus.

Another common reason is that it is due to some corrupt file in the system. It has a certain relationship with what we have commented previously, since it usually appears when we install a program and it gives some kind of failure or after some installation.

Steps to fix the error if Windows Defender won’t start

After seeing the main causes why Windows Defender does not start when we turn on the computer, we are going to see some steps we can take to solve this problem. The normal thing is that it is fixed without many difficulties just by carrying out a few simple actions.

See if any antivirus or firewall interfere

One of the main causes of problems of this type is having more than one antivirus installed. This is not a good idea, although some users may think that if they have two antivirus they will be more protected than having only one. In reality, what can happen is that a conflict is created and neither of them works correctly.

If for example you have Avast, Bitdefender, Kaspersky or any another antivirus installed next to Windows Defender, it is best to disable it. This way you will be able to check if the Microsoft antivirus starts correctly, since it could be being blocked by the other program.

Something similar could happen if we have a firewall installed. Sometimes it interferes with other security programs or whatever applications you have installed. We must verify that everything is in order and that it is not causing problems of any kind.

Check that everything is up to date well

Could there have been any error with some update? Undoubtedly this cause could cause Windows Defender to crash. It could have happened after installing an update of the antivirus itself or of the operating system and it has hung.

What we are going to do is go to Start, we enter Settings, we are going to Update and security and, once inside, it will start looking for new updates. They will also show us possible patches that have been left unfinished and that we will have to update manually.

This will allow us to have the equipment with the latest versions and thus correct possible errors that appear, but also make sure that nothing has been pending and is the cause of these blocks.

Scan for corrupted files

It can also happen that there are corrupted files in the system. This happens when we install a program and it creates a conflict or even a virus that may affect the registry. Sometimes there are corrupted files that prevent applications from starting such as Windows Defender.

This problem usually has an easy solution, since Windows itself has a command that we can execute. To do this you have to enter the Command Prompt or command line. We can go to Start, look for Command Prompt and run it with administrator permissions.

Once we are inside, we have to execute the scf / scannow command. This may take more or less depending on our equipment, the number of files, the power, etc. What it does is review possible corrupted files and correct them. Once finished we can restart the system and see if Windows Defender now starts correctly.

Check for corrupt files with Command Prompt

Is Windows Defender really activated?

This step is basic but it does not hurt to remember it. Basically what we are going to do is make sure that we have activated Windows Defender. Maybe due to some mistake at some point we stopped it. For example, if when trying to install or download a program we have temporarily disabled it.

We have to go to Start, we enter Settings, Update and security, Windows Security, Protection against viruses and threats, Manage settings and, when we are in this section, verify that real-time protection is enabled.

Windows Defender Protection On

Reset Windows to an earlier point

If everything we have explained has not had any effect, we can always reset Windows to an earlier point. What this does is return to a previous state in which everything worked fine. Points are created automatically, although we can also do it manually, and thus we can correct certain problems. Of course, it is convenient to save files that we have created recently.

To do this we have to go to Start, we look for Control Panel and then Recovery. There we have to give Open restore Sistem.

Open system restore

The process will start and it will show us a list with different restore points that have been created. We have to choose one from that list, which would be some time when Windows Defender worked fine.

In short, these are the steps that we can carry out if we see that Windows Defender does not start well when we open Windows. It is a problem that appears sometimes and is generally related to an update that has not been completed well or to a program that we have recently installed.

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