Go to Tools> Options and click the "Read" tab. There you will see the option to "Read all messages as plain text"—uncheck the box.
or
1. Click Start, point to Settings, and then click Control Panel. 2. Double-click the Internet or Internet Options icon, and then click Programs. 3. Make sure that the Internet Explorer should check to see if it is the default check box is selected, click Apply, and then click OK. 4. Open Internet Explorer, and then click Yes when you receive the following prompt: Internet Explorer is not currently your default browser. Do you wish to make it the default?