Hello Daniel,
Please verify the Jlink is connected with the red cable towards the pin 1 and 2 (see picture below). Also, if Jlink is properly connected and still not working, I would recommend you to use IAR IDE to flash the USB-KW24D512 board and make sure it is not locked or something similar.

If IAR IDE works, then I would recommend you to uninstall and install TestTool/BeeKit from scratch making sure you install it with administrator privileges (right click-> run as administration). If the device happens to be secured/locked, please use Jlink commander utility to unlock it as described in community post: https://community.freescale.com/thread/335458.
Regards,
AngelC