Found this on another site (it works!):
It's a really easy fix, which is just changing a default Hotmail setting for keyboard shortcuts. It takes 30s. Here's how to do it:
1. In Hotmail, look for the Options drop down menu. Click it and select More options...
2. Under the Customizing Hotmail subheading, select Keyboard shortcuts
3. Select the top radio button that says Turn off keyboard shortcuts
That's it.