Configuring preferences and options in Outlook.com
Try going in the back door. Sometimes when that happens to me I will right click the Outlook icon on my desktop and then click on one of the options there.... New Email Attachment, New Contact, New Appt. etc. From there it usually opens a window that you can have access to other windows in Outlook. I have also tried restarting my computer. I hate the new Outlook so kept the old but Microsoft has never really fixed this problem and now they're discontinuing any support for Windows 10 (which is where my Outlook opens to). Hope the above method/s work!