getting errors while loading the program into MCU

[AKr.1]

trying to implement a simple blink program on stm32f407vgt6, getting an error like device not connected.

earlier it was working fine with the same program, but now getting errors regarding this

kindly let me know the reason for this error

[Tesla DeLorean]

Hard to know,

Bad or low quality cables.

Hubs or Docking Stations.

Code which sleeps the processor, and turns off pins and logic internally.

Reconfiguration of PA13/PA14 and other pins related to the debug connection.

[Kamil Duljas]

Or bootloader mode :D check jumper related to BOOT0 pin