One of the most common reasons for getting a “404 – Component not found” error on your Joomla 1.5 front page is a missing default menu item. To resolve the issue kindly follow below steps.
Step 1: Login to Joomla admin area
Step 2: Go to Menus.
Step 3: Choose a menu item
Step 4: Set it as default by clicking the Default button at the top right menu.