Arduino mega 2560 and Ethernet shield stopped working

I setup and arduino mega and an ethernet shield to read analog and digital sensor readings, post the readings to an html website, and update a pachube feed. It was working perfectly without the analog or digital sensors or their power supplies connected, with it just uploading the base voltage readings off of the board to the internet. I then got the analog sensor setup and got it to upload the correct voltage readings, but when I brought it outside to finally hook it up to everything, the arduino mega board and I believe the ethernet shield stopped working. The problem with the mega is that it won't upload any code. I have tested it with the bare minimum example and can't upload, where as my uno does it almost instantly. Furthermore, when I run the simple webserver code with the uno and ethernet shield it doesn't seem to connect to the internet. Could some explain what could have possibly gone on, and if so, are there any solutions to this problem without buying a new board and shield. Thanks for your help!

anyone?

Do the leds light on the Mega, or is it dead? How are you powering it and the rest of the sensors? What input voltage? Is there 5v on the 5v pin?

The digital sensors are powered by the power supply on the arduino, and the analog sensor is powered by a 15 volt power supply with a 220 ohm resistor. The green light is on and the 5 volt and 3.5 volt power supplies are working. Thanks again

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The digital sensors are powered by the power supply on the arduino, and the analog sensor is powered by a 15 volt power supply with a 220 ohm resistor.

Can you explain what type of analog sensor, and how the analog sensor was connected to the Arduino?

I believe the sensor was a 4-20 ma sensor with a required 14-30volt power supply. I made a circuit between this sensor a resistor and the arduino at analog input 0 and the ground. I was successful in getting readings from the sensor with the sample analog serial input program.

Did the voltage on that input pin get higher than 5v? The 220 ohm resistor (if from the input pin to ground) should have kept the voltage low enough if that is all there is to the circuit. ??

The voltage was definitely higher than 5, but I don't the exact voltage. The analog sensor was working though.

I think the voltage was 10, but isn't the max voltage acceptable by the mega up to like 16?

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From the ATMega2560 datasheet under "Absolute Maximum Ratings":

Voltage on any Pin except RESET with respect to Ground ................................-0.5V to VCC+0.5V

Add: I measure higher voltages than that, but I use a voltage divider to reduce the voltage to acceptable limits. Test V+ --> 10K resistor --> Arduino analog pin --> 2.5K resistor --> GND

Now it will measure voltages up to 25v, but the voltage on the pin will be 1/5th the "Test V+" voltage.

If the device is 4-20ma output, the 220 ohm resistor should be connected from the Arduino analog pin to ground. In that case, the voltage on the pin should be less than 5 volts.

It was working perfectly without the analog or digital sensors or their power supplies connected, with it just uploading the base voltage readings off of the board to the internet. I then got the analog sensor setup and got it to upload the correct voltage readings, but when I brought it outside to finally hook it up to everything, the arduino mega board and I believe the ethernet shield stopped working

Well, I would put the board and shield back to the origional working state and see if it still works. If it does, then it is probably your wiring/power. If not, you may have damaged the board/shield.