That is my first post...
I am playing with arduino 2 weeks so please forgive me for any stupid questions.
I have the arduino uno R3 and I have a strange problem with the Ethernet shield w5100
I using the example code of webserver from IDE.
When I power the arduino up for the first time(power via USB) everything works perfect.But if I disconnect the USB and connect it again the Ethernet stop working.
The leb link is always on and all the other LEDs off.If I leave it for 10 minutes with out power and then power it up it ok.
I connect it to my Ethernet port of my laptop.
Please advice.
Do you think it is a hardware problem or something else.
Do you use the original Arduino Ethernet Shield? If yes, which revision (you'll find the revision number on the back side of the board "Ethernet Rx" where x is the number).
If not, provide a link to the shield you're using, there lots of them out in the wild.
We had a similar thread with these cheap Chinese copies. There the problem was in the ICSP connector that was too short to reach the underlying Arduino. Resoldering it a bit lower solved the problem for the guys there. Can you check that?
I using the example code of webserver from IDE. When I power the arduino up for the first time(power via USB) everything works perfect
That pretty much eliminates cheap clone issues.
I connect it to my Ethernet port of my laptop.
Have you tried connecting the arduino to a router instead to see if there are the same issues? The laptop connection is a wild card, and may be where your problem is.
OK, then try this server code. http://www.arduino.cc/playground/Code/WebServerST
If that does the same, then it may be a hardware related problem. Mine does fine after being unplugged for a few seconds. I've noticed really short power interruptions (< 1second) can cause glitches.
edit: Does the ethernet shield reset ok when you open the serial monitor?
Perhaps it is time for you to post the code you are using. The fact that you said the ethernet card will work as expected under a certain condition should eliminate a hardware issue with the ethernet card itself. The hardware part you control (wiring, type of connection, etc), what you are connecting the card to, and your code would be the suspect areas for issues.