ST-LINK/V2 USB Connection Error

[Park]

I connected STM32F401CCU6 board and ST-LINK/V2 with a SW called STM32 ST-LINK Utility. I'm sure it worked yesterday, but I don't know why it doesn't work now. The screen keeps saying "ST-LINK USB Connection Error" and plug in the USB and refresh, it will be connected for a while, and if I refresh, it won't be connected, so I think I'm going to lose my mind right now. I don't know what the problem is, what should I do?

[AScha.3]

>Do you understand me?

ok. - now i can see ...i have same F401 board here   and programmed with st-linkV2 stick (the "clone"), works fine.

you using st-linkV2 "original" (probably) now, here you have to connect 3v3 f401-board to 3v3 st-link.

it checking voltage , so when it shows 1,3v , it will not work. connect 3v3 and it should run.

(this is different on the st-linkV2-stick, it has 3v3 output and shows this voltage, so it works always)