Why wont the engine on a ford focus 1.6 start after timing belt has been changed?

If the engine on a Ford Focus 1.6 won't start after a timing belt change, it may be due to incorrect timing alignment during the installation. If the timing marks were not properly aligned, the engine's valves and pistons could be out of sync, preventing the engine from starting. Additionally, if the belt was installed too tightly or if any components were damaged during the replacement, these could also contribute to starting issues. It's essential to double-check the timing alignment and ensure all components were reassembled correctly.