Car sometimes won’t start, sometimes wont give me any power when stepping on gas

P0420 is almost always due to catalytic converter ineffective performance. You could have an exhaust leak influencing the code, you could have suspect oxygen sensors influencing the code. But almost for sure the catalytic converter (bank 1) is at fault for premature wear out -- perhaps likely caused by other vehicle performance concerns, such as fuel consumption issues causing catalyst over-temperature. The P0174 code does indicate "lean" fuel conditions that would lead to increased fuel into the engine, and in turn - into the exhaust. Hands on inspection and diagnostic testing is needed. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops