I write the Ubuntu 12.4 .iso file to CD. reboot my PC and boot from CD and chose install Ubuntu. I don't know why the chosen "upgrade Ubuntu 11.10 to 12.04 " is disable ? is problem in my hardware? I read all the page for this upgrade on the internet but none of this worked for me
You will not see an upgrade button unless you bring up Update Manager. Below are different ways that can help you in your process.
Use this method if the system being upgraded is not connected to the Internet. To upgrade using a CD or DVD See Upgrading Using the Alternate CD/DVD
Otherwise you can
From the desktop Press Alt+F2 and type in
First check for updates, then Install them, and finally click Upgrade and follow the on-screen instructions.
See https://help.ubuntu.com/community/PreciseUpgrades for details.