You may have disabled Toolbar through the Add-on Performance Advisor, an Internet Explorer feature which allows you to disable add-ons to help your browser run faster. This dialog box may sometimes appear at the bottom of your screen when you open Internet Explorer. Clicking “Disable all” will disable all add-ons, including Google Toolbar, which has been optimized for performance on Internet Explorer 9.
To ensure that you don’t disable Google Toolbar inadvertently in the future, you can individually select particularly slow add-ons to disable when you see the Add-on Performance Advisor dialog box appear. You can enable Toolbar by following these instructions. If you decide you don't want to use Toolbar, you can uninstall it at any time.