can't debug code using st link

[Sabarinathan1]

Hi community @STTwo-32 ,

I am using stm32f407vet6 board I am new to stm32 board.I wrote an Hello world program in STM32cubeide and i try to debug the code.I bought an ST-link v2 from online.when I try to debug the code it says frimware upgrade require.I upgrade the frimware in DFU mode then it shows this error

and I watched a youtube vedio where he use st-link utility software and he instructed to connect under reset mode and use full chip erase.But when i try to connect under reset mode it shows this error message 

i also tried stm32 cube programmer 

it says not connected on the top right and also target voltage 0.i also checked power connection and connection between st-link and my board.

[Imen.D]

Hello @Sabarinathan1 and welcome to the Community

What does your ST-LINK look like ? Make sure that you use a genuine ST-LINK/V: How to recognize a genuine ST-LINK/V2 versus a cloned one.

Check all pins, jumpers, Debug pins and make sure that there is no conflict with other pins.

Refer to the checklist in this article that will help you to fix such issue:

How to solve connection errors when connecting and programming the STM32 target board

[CTapp.1]

If it is a genuine ST-Link, then I've seen this in the past and needed a reboot to fix.