To approach troubleshooting an instance in OpenStack that’s failing to launch, I would first check the instance logs using the `nova console-log` command to identify any errors during the boot process. Next, I would verify that there are sufficient resources available, like CPU, RAM, and storage, and ensure that quota limits aren't being exceeded. I'd also review the network configuration using Neutron to make sure everything is correctly set up. If the issue persists, I'd investigate the compute node's status by checking the Nova compute logs for any hardware or service-related problems. Ensuring compatibility between the image and the selected flavor would be another step, as well as reviewing security group rules to rule out any blocking issues. Finally, I’d make sure all OpenStack services are up and running smoothly and cross-check any findings with the OpenStack documentation or forums to see if it's a known issue. This approach reflects my methodical and thorough process in troubleshooting cloud infrastructure issues.