Outlook has become very unstable

My Outlook 2007 has become very unstable when I am composing an email message. What happens is that while I am typing, the screen suddenly changes to an entirely different screen that shows another Outlook feature, such as Contacts. When I click the Outlook icon in the Taskbar, the two screens show up side-by-side. When I click the New Message screen, the message I had been typing shows up, and I can continue typing until the next time.
However, there have been times when I clicked the New Message screen and I would discover that an entire paragraph was missing.
Any ideas? Thanks.

 

MS Office has a self-repairing function. For Vista or later right click Office in Control Panel > Programs and Features and click Change. Select Repair.

 

Thank you, Earthling, for your quick and helpful reply. I followed your advice and I think the problem has been solved. After using the repair tool, I composed a test message of some length and did not experience any difficulties.

 

Thanks for feedback frybo