Outlook 2011 stops working when I’m writing emails

This has happening the last 2 weeks: I open an new message, start to write it and then I cannot do anything anymore in Outlook. It gets in a loop where I cannot finish writing nor access any Outlook commands (the cursor stays "rainbow running"). I must then restart the computer and when I open Outlook again, it says it has saved a draft of my message. All very time consuming and no work done...

Any idea of how I can fix the problem?

Many thanks