hi sir i am writing data in to flash in stm32f031c6t device at address 0x08005000 my data gets saved properly and code works properly but problem is after one time reset of mcu program dosent run

The chip boots up to 0x08000000 and your code is at 0x08005000. Either recompile and move your code to 0x08000000 or you'll need a bootloader at 0x08005000 to jump to it. I'm fairly sure you can remap the vector table on this MCU but not 100% sure.

Make sure BOOT0 is low during reset.

Going to need to do some debugging and critically analyze what you're doing and what the processor is doing. Processor is almost certainly running code, perhaps yours, perhaps not. Make sure to instrument your code from Reset_Handler on in, and also Error_Handler() or HardFault_Handler() if it ends up in those routines.

+1 on the BOOT0 pin state, or related option byte settings.