New Teensy appears dead?
We saw this recently. A brand new Teensy straight from PJRC (the company that designed and makes them) appeared to be dead. No USB COM port was visible. Pushing the programming button on the Teensy did cause the programming LED to come on but still it never presented a COM port.
After trying a number of things, I was almost ready to call it dead when we brought up the programmer application, teensy.exe, opened a hex file built with the grblHAL Web Builder and pushed the programming button on the Teensy. Lo-and-behold, it programmed the Teensy and all was well. It turns out, this is normal behavior with new teensies. Why, after literally thousands of teensies, I have never seen this is a bit of a mystery to me. When using the Arduino IDE (with "Teensyduino", the PJRC programming add-on), it takes about 10 seconds to see the COM port. The Teensy supports the HID (human interface device) capabilities of USB and initially presents that way to Windows. Cleary, there is some back and forth going on to create the USB COM port. Teensy.exe is necessary for that. So, if you find yourself in the situation where there is no USB COM port showing when you connect to a new teensy via USB:
You should see teensy.exe quickly flash "Erasing..." followed by "Programming...". It will be very quick so you might miss it. The LED next to the USB socket on the Teensy will flash for a few seconds. The Teensy is ready to test with your GCode sender of choice.
I'm Phil Barrett, a long time CNC enthusiast. I run a small company, Brookwood Design, that makes several breakout boards for grblHAL and love to help people get the most out of their CNC machines.