2008 Prius engine won't start, red triangle after radiator replacement

I'm trying to fix a Prius that was in an accident. The accident damaged the radiator and inverter coolant circuits and the AC condenser causing loss of both fluids.

The radiator, fan assembly, inverter mounting brackets, air intake cleaner box, throttle actuator wiring harness, and the inverter coolant reservoir have been replaced. I've filled and bled the inverter loop with OEM coolant.

The 12v battery was entirely discharged since it has been sitting for weeks so I had to jump it. I tried to start the engine so that I could bleed the engine loop, it sounded like the engine was failing to catch and I heard a knocking/clacking sound accompanied by the red triangle. It did go into ready mode but the engine wouldn't start. I have tech stream on my laptop but haven't had a chance to hook it up yet. Any ideas what it could be? What should I check first?