Hi Simon,
I have the same issue and I also have a Mega2560:
WiFi shield not present
WiFi shield not present
Also, my wifi shield already came with the green wire on the back.
I tried to upgrade the firmware with the github version without success:
ludo@titan> sudo ./ArduinoWifiShield_upgrade.sh -a ~/src/arduino-1.0.2 -f all
Arduino WiFi Shield upgrade
=========================================
Disclaimer: to access to the USB devices correctly, the dfu-programmer needs to be used as root. Run this script as root.
****Upgrade HD WiFi module firmware****
dfu-programmer: no device present.
dfu-programmer: no device present.
dfu-programmer: no device present.
Remove the J3 jumper then press the RESET button on the shield then type [ENTER] to upgrade the firmware of the shield..
****Upgrade WiFi Shield firmware****
dfu-programmer: no device present.
dfu-programmer: no device present.
dfu-programmer: no device present.
Done. Remove the J3 jumper and press the RESET button on the shield.
Thank you!
I also observe something somehow troubling, the L9 LED turn off quickly after the board boot. Worst, if I hold the wifi shield from the side (with my finger) the L9 turn on. I know..
I have similar behaviour with and without external DC power.
Please notice this is my very first attempt playing with Arduino, so I am definitely a newbie.
Finally, yesterday (the first time I use it), the wifi-shield was working fine (I could run the WPA example) and connect my network.
I will look at this again tomorrow, good night! :-)