Resolved! STM32F765 EXTERNAL CRYSTAL
I have custom stm32f765 board it has very minimal design. only some caps and resistor for the reset and boot. My problem is i have attached hse crystal of 16Mhz.this one https://www.digikey.in/product-detail/en/epson/TSX-3225-16-0000MF09Z-AC0/SER4069...