The answer to 'my mini split won't turn on' is that there could be several common causes, such as a tripped circuit breaker, issues with the thermostat or remote control, or a problem with the indoor or outdoor unit. First, check the circuit breaker and reset it if it has tripped. Then, inspect the thermostat and remote control to ensure they are powered on and set properly. If those don't resolve the issue, there may be a problem with the indoor or outdoor unit that will require a professional HVAC technician to diagnose and repair.
Mini split systems are complex and have many components that could fail, so it's generally best to have a professional HVAC technician inspect and repair the system. Attempting to troubleshoot or repair a mini split on your own can be dangerous and may cause further damage if you don't have the proper training and expertise.