The information below is copied from Google support:
Internet Explorer has a Compatibility View, a feature that affects how some websites are displayed. If Compatibility View is enabled for google.com, it may cause some Google Mail features to display incorrectly. So, we suggest that you remove google.com from your list of sites that have Compatibility View enabled to ensure that Gmail displays correctly. To do this, follow the steps below:
When you close the Settings window, the page you're on will refresh and display in normal IE8 mode.
If you don't see google.com listed or if these steps don't help you resolve the problem, please make sure your computer has the latest Windows updates.
Known Issues >