You need to enable the interrupt also in NVIC (interrupt control registers):
NVIC_EnableIRQ(USART1_IRQn);
NVIC_SetPriority(USART1_IRQn, 14);
You need to enable the interrupt also in NVIC (interrupt control registers):
NVIC_EnableIRQ(USART1_IRQn);
NVIC_SetPriority(USART1_IRQn, 14);