Port not recognised when plugged into arduino IDE and computer makes no sound when I plug teensy and shield in like it should when any USB device is plugged in so fairly sure I have fried the teensy somehow
There's one thing I've done to revive an unresponsive Teensy: hold down the program button as you connect to USB. I think that triggers the bootloader chip to do something special to revive the main microcontroller, but I don't recall the details.
also, if I don't cut trace on next teensy, I will need to connect both USB and power to shield in order to make the matrix work?
In that case, you can probably just apply USB power to program the sketch. There is a chance that if there are a lot of LEDs driven by the panel while you're programming, it could draw too much current from USB and cause a problem, but this is unlikely.