Why won't my Vauxhall Astra start?

I recently purchased a used Vauxhall Astra and have been having trouble starting it. It has a new battery but still won't start. What could be the issue?

One possible reason could be a faulty starter motor. It may need to be replaced.

Another possible reason could be a faulty alternator. It might not be charging the battery properly.

It could also be an issue with the fuel pump. If it's not delivering enough fuel, the car won't start.