Make sure all your drives are clear of disks/floppies etc and reboot. If this does not work, press delete at boot up, entering the bios, move the arrows along in the bios till you get to boot. What is your first boot devise, Post back.
Sorry dont recognise your 1st boot devise. Write it down. Set 1st boot devise to your cd drive. Put in your win xp disk and boot. if it still wont recognise the disc, boot again pressing F8 and highlight your cd drive and boot again. the computer should now start to run the operating system. post back