I just installed ubuntu by dual boot. but neither my internet nor ether net cable works.
It works fine when i boot from life usb.
I thought ubuntu installs your drives/
what should i do?
Try to run"sudo lspci" in a terminal window, it should show your NIC's brand and type.
Try "sudo lsmod" too - it will show if any network driver modules are loaded by the kernel.
A thread you might find helpful: http://ubuntuforums.org/showthread.php?t=25557
I think you might have fixed your problem ready (by switching from Ubuntu 11.04 to 11.10)...
I hit problems with by ethernet card, an Atheros AR8161 Ethernet card, when I installed Ubuntu 11.04. To fix it I had to for the new driver and built it myself.
In my case the wireless network driver was working OK, so I was able to download what I required easily enough. But I could equally well of used a USB stick from another computer, or even booted into Window (I'm dual booting), downloaded the file, and switched back to Ubuntu and grabbed it off the NFS partition.