The answer to 'my panel upgrade won't turn on' is that there could be several common causes, including a tripped circuit breaker, loose connections, or a faulty main breaker. Symptoms may include the panel not powering on at all or certain circuits not working. Solutions can range from resetting the breaker to replacing the main breaker or even the entire panel, depending on the issue.
If the panel upgrade is not powering on, the first step is to check the main circuit breaker. Try resetting it by switching it fully to the 'off' position and then back to 'on'. If that doesn't work, you may need to call in a licensed electrician to further diagnose and repair the problem. Attempting to work on the electrical panel yourself can be extremely dangerous if you're not a trained professional.