Neither firmware I'm able to install work

So, at my school we have been having issues with our Cortexes. Any Cortex we try to set up doesn’t work and has some issue. I’ve found that if we install firmware on both the Cortex and the Joystick using the VEXnet Firmware Upgrade Utility, it works properly between the two but, the second we try to download a program to the robot it gives the error, “Cannot communicate with VEX Cortex Slave CPU. Master CPU is working.” If we try to install firmware from RobotC, We find that it says “No communications link available to VEX device.”(Even when connected with a A-A USB cable) when attempting to install it to the Joystick. We are able to install to the Cortex and download programs, however when running it, the Game and Robot LEDs always flash green and the VEXnet LED remains silent. We’ve tried every program we could find and even 3 other computers, No matter what we do we are unable to get this to work, despite the fact that we had it running smoothly previously.