I Can not access bootable cd

Hello,

My name is vijay.I firstly try to install windows xp but during installtion i lose set up and i can only install half of xp now i want to install full xp but my cd rom can not detect bootable cd of xp.And when i double click on cd-rom it give me an error message that :"G:\is not accessible.Incorrect Function.I can not also setting booting priority when i restart so pls also tell me what is the key of booting setting.I have a toshiba laptop.So pls give me an approprite answer for these problems.