When you double-click the avast! icon (blue circle with white "a") in the system tray, the On-Access Protection Control opens. Along the left side is a list of installed providers. Selecting each of these providers in turn displays its status on the right side. There are also buttons for starting (enabling), pausing and terminating (disabling) the selected provider.
If you right-click the avast! icon in the system tray, the last item should be Stop On-Access Protection, which stops all providers. Clicking the last item again restarts all providers. There are also options in the right-click menu for pausing, stopping and resuming individual providers.
Ken