My Arduino 2560 Power on, Won't upload

I just bought an Arduino 2560 Board, I was using it with windows 7 and it was working perfectly.

The problem is that now the Arduino is not detected by any of the operative systems, I am currently testing with Mac Snow Leopard, Linux and windows 7. The reset botton is working, and when I plug it to the computer the Power LED turns on......

Any suggestions on how to fix this? 



Is the board not recognized

Is the board not recognized by the OS, or just not connecting in the Arduino IDE?

When using Windows, do you hear a beep when you plug it in to the USB port or get any other indication that the OS has recognized a USB device has been plugged in?

Have you plugged (or unplugged) any other USB device into the computer since it was working with the Arduino before? After plugging in your Arduino to the USB port, try opening Windows Device Managers and checking to see if the port has been listed.

If you can get past the OS recognizing the board, verify the Board and Serial Port settings in the Arduino IDE.