Hey @potatonet, if you are on Windows you might try following this guide to make sure your driver is installed correctly: https://community.spark.io/t/installing-the-usb-driver-on-windows-serial-debugging/882
If you uninstall and remove all drivers first, you can also try installing the Zatig driver which works for local development and serial over USB. http://zadig.akeo.ie/ You’ll want to install the WinUSB driver for the Spark Core with Wifi when it shows up in the main dropdown box.
Also it needs to be in Listening Mode before it will try to connect over serial. This is a slow flashing Blue LED. You can reset the device, and hold the mode button until you see the blue LED, then let go. Make sure your Tera Term is closed while you are doing this… then open it and try to open your serial port at 9600 baud.
Also as a user of the Spark Core, I’d like to say that 
Spark Devices is a startup, and their support is by far some of the best support I’ve seen from any company! 
This growing community will be sure to impress you as well!