I understand now.
Do you see a new port in the Arduino IDE's Tools > Port menu after you plug in the Mega?
If not, make sure you have the USB cable fully inserted into the Mega and the PC.
You may have a damaged/defective or charge-only USB cable. Try a different one.
USB 3 ports can sometimes cause problems. Try a USB 2.0 port or a USB 2.0 hub connected to a USB 3 port.