zeroG:
The ethernet connection is not working, the "unknown device" appears and disappears rapidly from the connections menu, and if i type in my browser http://192.168.240.1 or http://arduino.local it can't find the page.Now the wan led (yellow) is blinking, sometimes the wlan led (blue) blinks for a while and the usb led (white) goes high every 5/6 minutes for 1/2 seconds.
zeroG,
to me it sounds like your Yun is stuck in the boot process. There is a way to fix this.
We need to diagnose the issue.
With the YunSerialTerminal, type ifconfig and post that.
Then type, type iwconfig and post that.
Depending on the results we will know, where we are and if we can fix it.
The first command will let us know if your ethernet is working and what the IP is.
The second will let use know if the wifi is okay.
Jesse