Follow these steps to resolve the issue of Outlook not opening attachments:

1. Check the file type that you are trying to open. If possible, convert the file type to a format that is supported by Outlook, like JPEG, PDF, HTML, MP3, etc.
2. Check if the file is blocked by Windows. Go to Windows Control Panel > Security Settings > Trusted Sites > Unblock. This will unblock the file from Windows and then allow it to open in Outlook.
3. Ensure that the attachment is not exceeding the maximum allowed attachment size. Outlook may be set to not display attachments exceeding the default size.
4. Check for any virus or malicious software in the file that may be causing the issue. Make sure to scan the file before opening it in Outlook.
5. Disable any security settings on your device if they may be blocking the attachment from executing properly.