Right click your network management icon and select "Connection information." There should primary and secondary DNS IPs. Can you ping them? If I do a shutdown on my box, when I reboot the old DHCP settins are used. If I also cut power at the power strip, DCHP seems to work correctly. I guess powered down isn't always completely powered down. My connection is over a Comcast cable modem which I always leave powered up.

Yes, I know. Output is from after selecting this.

Both IPs are 0.0.0.0. As a matter of fact, everything except for "Hardware Address" is 0.0.0.0

This is some output from dmesg:
Looking at the output of lspci, this device is my Ethernet controller:
Could this be the problem?

This was indeed the problem. I booted with the parameter acpi=off, and now I've got no troubles connecting. I remember now I had to fix my DSDT for this laptop. Thanks a lot for the help everyone.

Sorry to raise the dead, but would anyone kindly explain what merchtemeagle did to solve not being able to connect to the internet? I installed Ubuntu over at my aunts house and since Im really really new to linux I really had no idea what to do and pulled out a chunk of hair .

When you start your machine, you are supposed to fall on grub (bootloader).
Then you need to type "e" to edit the line kernel= blabla...
Go to the end of the line and add acpi=off, followed by enter
Type "b" to boot.

If this solves the problem, then you will need to make it permanent.
If this doesn't, open a new thread because it's something else.

ok sweet thanks, Ill have to wait till maybe tomorrow to try it out, but Ill be back for sure XD

I have what I believe is a very similar problem to what was encountered here, but the difference is that my connection works at first and then will die suddenly. It also only seems to die when I am using the connection. This is on a new Ubuntu installation onto a new desktop pc that I just built. (Asus P5K WS, Intel Core 2 Duo).

When the computer first comes on and I do an ifconfig -a, I can see information for eth0 and lo. eth0 has a inet addr and everything works fine. Here are the instances that I've noticed the computer losing its network connection, at which point all connectivity is lost. Trying to do an ifdown/up does not work, and the results are identical to what was seen in the prior posts. I have lost the connection several times when transferring lots of data from Windows Vista (using samba), and also during an SSH session from work.

Once the connection goes down, ifconfig -a returns the exact same results as in the first post. There is now an eth0:avah listed that has an inet addr of 169.254.xxx.xxx. This seems really odd to me as how this "new" interface would suddenly appear. I'm also using DHCP through my router. Do you think that ACPI could also be the culprit here? Why would the connection suddenly drop out when it is actively being used, and then lose its IP address?

I've experienced some lost connections with Comcast cable that turned out to be my cable modem. When you loose a connection try calling your ISP and seeing if they can ping your modem. You could also take your router out of the picture and connect direct to the modem. If it is your modem you will be able to ping your router which would imply that the issue isn't in the PC.

I do not think it is an issue with my router or ISP provider, as the other pc's on my network still work fine. Also, a reboot of my Ubuntu machine fixes the network interface and allows it to again connect to the network. I'm thinking that somehow my NIC is losing it's IP address and then for some reason can not get it back. I'm stumped as to why it just randomally loses it, however, and only seems to do so when the NIC is being utilized.

I have edubuntu-6.06 installed on my PC (PIII 184MB RAM), because of higher sys requirements with ubuntu or kubuntu.
iam using Sis900 Ethernet card and cable modem (Motorola SB5100) to connect to internet(broadband) in winxp. somehow iam unable to do that same using ubuntu. I had the computer connected to my cable modem during install and I hoped that the networking would be setup automatically, because I'm a complete noob.
I have been booting the computer and logging in while connected to my cable modem but a network monitor applet shows activity and so do the lights on my modem but when I try to access the internet using browser it shows error downloading the page!!.
from the forums i gathered that i have to do these things and so i did:

1. enable DHCP in the network settings applet(system>administartion>networ)
2. put the modem in stand by and run dhclient it gave me an ip after that turned the modem on
3. ran pppoeconf and supplied username and passwd that i use in xp for connection
4. after that pon dsl-provider

If anyone knows how to get ubuntu to connect to the internet please advise, in detail. Thanks.

I can't speak for India but in the US, pppoe is only used with DSL. Cable is a strait LAN connection.

thank you for that reply!!
i don't know if i got it wrong, heres how my connection works in xp:
i am giving you a read-out of my 'network connections' in windows
Snapshot of 'network connections'
as you can see that the computer says that it is using a pppoe device for connecting to internet and i did run pppoeconfig in Linux but to no avail...i can't even ping any outside servers(tried google 216.239.37.99) of course the i can get to the cable modem's configuration tool (192.168.100.1). i even tried turning off the acpi (as suggested at the boot time, sis900ethernet card)
thanks in advance

I'm using the same cable modem as you with Comcast cable. I didn't know about 192.168.100.1 -- works for me as well. I suggest you contact your ISP and double check pppoe, regardless of what Windows says. You could also ask them to ping your modem which they will probably want your modem MAC address to do. The modem MAC should be on the bottom of the modem on a sticker.