trouble installing ubuntu from dvd and usb

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http://askubuntu.com – i currently run windows 7-32 bit..i downloaded ubuntu 12.10 iso from http://www.ubuntu.com/. then i burned it to a dvd..i tried to install it..every thing goes fine utill i reach the option *install ubuntu alongside windows 7*then on clicking continue dvd ejects itself and "please remove the installation source or the tray "appears on the screen..and again windows starts and the installation remains incomplete...i then created a bootable usb and tried to install but again on the same option installation stops ...i m not so advanced user to try something else option. i tried to use it but i don (HowTos)