pca10040 cannot be found during keil download

[kanchun]

keil cannot find the board.  

It was ok to start with but cannot find the board after erased a few times.

[Bjørn Kvaale]

Are you using Windows 10? Can you find the nrf52 dk in file explorer as a JLINK drive?

[kanchun]

Yes, it is win 10 and cannot see the jlink drive.

When the board plugged in, it say cannot recognise the USB device.

[Bjørn Kvaale]

Could you try holding the IF BOOT/RESET button, turn the device off & then on. Then, the board should show up in Bootloader mode (BOOTLOADER) as an external drive. Then, download this file (choose the latest one) & drag & drop it to the BOOTLOADER external drive. Then, if you power cycle the board, it should show up in file explorer again.