Question about NZXT H9 Flow

theoretically yes, but you can't be sure, ATX is actually a standard, but unfortunately not all manufacturers adhere to it, so you would have to check the placement of the motherboard screws on your motherboard as well as the screws on the power supply unit to see if it corresponds to ATX. you can find the standard on the internet if the screws are as specified, then you can do it. if HP has done something with special dimensions again to prevent a repair or replacement, you will probably stay with your old case.