Hi Derek,
When I do a POR, it does not show up in my COM port. Then I am not sure if our board hardware's problem or my configuration's problem.
One more thing is that, on our board, we don't have the USB-OTG chip.
Then the connection is just as shown below.

I measured the VREGIN is 5v, but USB_D+ and USB_D- are all about 50mV.
I read that when it is plugged into the PC, the USB_D+ should be pull high.
Is there something wrong with this connection?
Thank you.
Daniel