I have problem to connect internet with natty. cannot even ping router anymore

[Shuanghe]

Hi all,

I installed Natty from day 1 and everything worked fine. I actually like
Unity more than the former Gnome look. :-)
However, a few weeks back, my pc would just loose internet connection
sometimes without reason. Usually after reboot it would work fine.
Today however, I couldn't get it to work anymore even rebooting system lost
its charm. here's the situation:

I have both my desktop (wired connection to router) and laptop (wireless)
with natty. I cannot connect to my router (ip 192.168.1.1) by desktop or
laptop.
My HTC smartphone has no problem of surfing the web using wireless and my
company's pc with Win XP also works fine with wireless.
I even connect to the route by its ip 192.168.1.1 under Win XP (wireless).
So I have to say the router's fine. The problem lies somewhere in the natty.

So I googled a bit and some web suggested the router didn't get ip etc. I
tried everything I could find. Nothing worked. Can anyone help me with this?
what information do you need? Any help would greatly appreciated. I really
need to get the desktop working.

cat /etc/network/interfaces
auto lo
iface lo inet loopback


I even added the following as suggested by some web. no luck there either.
auto eth0
iface eth0 inet dhcp
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