Why is my Vauxhall Insignia not starting even though the battery is fully charged?

I have a Vauxhall Insignia and I recently replaced the battery with a new one. However, the car is still not starting. What could be the problem and how can I fix it?

Check the battery terminals for any corrosion and clean them if necessary. Sometimes even a small buildup of corrosion can prevent the car from starting.

It could also be an issue with the starter motor. Try tapping on it with a hammer to see if it starts. If it does, then the starter motor may need to be replaced.

Make sure all the electrical connections are secure and tight. Loose connections can prevent the battery from properly charging the car's electrical system.