Hi, I'm new to arduino. I'm using a arduino duemilanove board with Atmega328 PU. Everything was working fine until today. Now the problem is that the arduino pins can not take a very small load like 1 mA. After configuring every pins as OUTPUT and assigning them HIGH and LOW state, I have checked the output voltage level with multimeter, its perfect i.e 4.9 v for high and 0 v for low state. But when I connect a small load like a LED with the current limiting resistance in pin output set as HIGH, the output voltage is dropping down below 2.4 V . This is happening with every pins except pin 13. Is there any solution for this or the board/micro controller is damaged permanently?
Hi, when you do this test, measure the 5V pin on the arduino, see if it drops as well.
Tom..... 
But when I connect a small load like a LED with the current limiting resistance in pin output set as HIGH, the output voltage is dropping down below 2.4 V .
What colour LED and what value of resistor.
This sort of thing happens when you do not set the pin as an output but you say you have done this. Please double check.
Please post your code. Please be certain that it's precisely the code that you're using in your tests.
Possibilities:
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Your power supply have a large internal resistance. If you used a wall-wart type power supply or USB maybe the wiring is dodgy, the wall-wart is near overloaded, or you have approached the load limit of your USB port. If you used batteries they may be dead and requires a replace/recharge.
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Your current limiting resistor for the LED is too large. Usually when directly driven off an Arduino pin, the current limiting resistors I used are 47 or 68 ohms. If you went with 1K it is too much.
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If all this is not sorting out for you, maybe you got one of those dodgy clones with fake chips. Try use the pin to drive an 2N7000 MOSFET and control your LEDs with those. (and remove those current limiting resistors when using 2N7000, as those MOSFETs won't be fully on with 5V yet)
technix:
3. If all this is not sorting out for you, maybe you got one of those dodgy clones with fake chips.
Which ones are those?
AFAIK there's no such thing as a fake, working Atmel chip.
. Your current limiting resistor for the LED is too large. Usually when directly driven off an Arduino pin, the current limiting resistors I used are 47 or 68 ohms. If you went with 1K it is too much.
Yes 1K will be too high but 47R will be too low. Anything from 40mA up damages your arduino output pins.
and remove those current limiting resistors when using 2N7000, as those MOSFETs won't be fully on with 5V yet)
What current limiting resistors? Not the ones on the LEDs.
As a gate of a FET draws no current a series resistor does not matter. It only limits the current on switch on or when you are applying PWM to the FET.
At a 5V gate voltage and 50mA current the drain source resistance is typically 1.7R so it is very close to being fully on. At 10V gate voltage and 500mA the drain source is typically 1.2V.