The last couple of days I've been using my Arduino again. At first everything went fine, but now I'm running into some trouble I'd like some advice on.
I have an Arduino Duemilanove to which I have attached an Ethernet Shield (without SD-card slot) and a small I2C OLED display. Trying to demo my project to a friend yesterday the Arduino kept shutting down after a few seconds. I have tried different power sources, PC via USB, external adapter at different settings (4.5V, 6V, 7V). Using the external power connector I do get a power light, but my display doesn't turn on. Using power supply via USB it turns off after a few seconds... Windows doesn't recognize the USB-device in this configuration and makes the 'USB device removed' sound when the Arduino turns off.
When I remove the Ethernet shield it takes a little longer before the Arduino shuts down. Also, Windows does recognize the USB device and I'm able to upload new software.
What could be wrong and/or what tests or measurements could help determine the problem? I'm not very familiar with electronics so I'm sorry if I'm overlooking something really simple here.
Kind regards, Chris