You at least need a bootable disc or recovery disc or else formatting the computer will be of no use you can’t reformat the computer without the bootable Windows XP CD or try to get it from the dealer of your computer.
Another option is try to restore your computer at a previous date by clicking on the Start button and select the programs from the Start menu and after that select Accessories and click on the system tools and you will see the following item System restore and click on it and you can select the previous date when the system was operating very well.