I am trying to power up my new Mega 2560 board through the USB connect to my PC. I have tried two different cables. I also have a Max32 which powers-up ok from the same USB port. Do I simply have a bad board or is there something I can further do to check?
What are you expecting on a "power up"?
Does the computer go boop-boop when you connect? Does it show up under Ports in Device Manager?
If Yes, connect D0 to D1, and Reset to Gnd. If you open the IDE, select the Port that is the board, and the Serial Monitor, is text you type in copied back?
Arduinos come with the blink sketch pre-loaded. That's probably what you are observing.
The power LED should be on and the L led will be flashing as the result of the blink sketch.
Which operating system do you use?
Do you have a clone or an original? What does the chip closest to the usb port look like? Is is a square with legs at all sides? Or rectangular with legs at two sides? The latter would need a driver.