You probably need to belong to the dialout group in order to access the /dev/ttyACM* ports. Try the following.
In a terminal, with the board plugged in, enter:
ls -l /dev/ttyACM* , with the board plugged in it will show the group that has access rights to the port.
Example: crw-rw-r-- 1 root dialout ... /dev/ttyACM0, root is owner, dialout is the group with access.
If you don't see any ports you may have a defective board or USB cable.
Entering the command, groups, in a terminal will show the groups you belong to.
sudo adduser YourUserName GroupToJoin Will fix things if you need to join a group, logout and login after you run adduser.