My computer is Pentium 4 and not at working properly because of VIrus and that's why I want to format it, but when I restart it is not showing the option of DEL for setup but it is directly opening the OPerating system XP. What should I do ? Help me??

You'll need to access the BIOS in order to make the PC boot from the CD. The button used to access the Setup/Bios differs depending on the make and model of the computer.

If you want to format it, you need to boot from someplace other than the hard drive. This could be a floppy or CD drive. You then need to run the Format command from the boot disk.