Michi-san,
Just adding to Gautam's reply, are any of the LEDs on the emulator lit when you connect it to the USB port? Check the unboxing video that shows this.
If not, then I think the emulator is somehow not getting enough power from the USB port (as you said it works in someone else's PC).
If they are lit, then it is possible the device drivers may be at fault. You could try to uninstall and reinstall them (check this thread for some insights).
Apart from this I am really not sure what may be happening in your case. Per your description it really seems that things should be working.
Regards,
Rafael