First, connect the USB to the computer and the machine, then power on the printer, then select USB Online Printing by slicing Print
Not sure if I know what you are meaning by "select USB Online Printing by slicing Print". I am using Simplify3D. Not like the old opensource 3D printer controls. You don't pick slice and send.
Might be a wrong baudrate. I work for a company and they have everyone's computers locked up like Fort Knox. You have to be an administrator to change even something as simple as a baudate. I will get with the IT guy and seen if that is the problem.