Can't find the USB dongle in SmartRF Programmer

Hi.

The red LED is off now on CC2540 USB dongle, and my PC can't detect the device now. I can't find it on the list in SmartRf Programmer, when i insert the USB dongle in a port and the debugger in another port. I have connected the debugger and the dongle with the flat cable, but the software only shows the debugger as a device in the list. 

What to do ?

Thanks in advance