All works with with my basic Arduino until I try to connect a simple project with the HC-SR04 sensor to my computer through the USB. I have the left pin to 5 volts and the right pin to ground. The middle two pins are connected to digital pins on the Ardino. When I try to connect, the USB connection is not there. When I try to set up the circuit while attached, when I connect the 5 volts the lights go out and the USB goes dead. I tried attaching the board to a 9V battery and it got hot. Perhaps a short, but my circuit is so simple I don't see how this is possible. thanks for any thoughts...
Most likely a wiring problem or a defective module. When powering the arduino board on Usb there is a on-board 500ma thermofuse that opens up removing power from the board and killing the usb link if anything in your project is trying to draw more then 500ma of current. That is to protect damaging your PC. Without a schematic drawing of your wiring and a Link to your specific sensor type, it's difficult to see what and how you have everything wired up, so it's hard to check your work.