How is the raspberry pi connected to the router? Have you used it for other projects in the past? What are you using for storage? Is the storage name brand or the cheapest thing you could buy? Did you use the storage for something else first? If yes how long? Have you connected the raspberry pi to a monitor and checked the logs/ made sure it's running properly? Did you set a static ip address in HomeAssistant or set a static reservation in your router?
What steps have you taken to troubleshoot?