pc format problem

Killdisk:
http://www.killdisk.com/
Install it onto a floppy or cd. Then run it when you re-boot. Find your disk and then follow the instructions, it will take at least three to four hours to wipe your drive so be patient. When it is done re-boot your system. Take out your disk. Your computer will now say "No system found, insert system disk and press enter" or something similar. Now put in your Windows disk and press the "Enter" key on your keyboard.
Hope all goes well.

OR:
you can download a linix operating system like ubuntu:
http://www.ubuntu.com/
Burn this to a cd and install it. When finished re-boot with your Windows disk and follow the instructions. Make sure you have your Windows key with you.

Insert your Windows installation CD. (Make sure you have your product key handy.) Reboot the computer. Make sure your CD drive is set first in BIOS for boot priority. This is easy to do.

When you turn your computer on it should flash a Dell or Sony or HP screen...whoever the manufacturer is. If you look it should say press F1, F2, or F10 to enter setup. Each manufacturer is different, so it depends on who it is. Then you can arrow over to boot priority or boot options and make sure the CD drive is listed before the hard drive. Save changes and exit.

Now you will enter the Windows setup screen. Your first options will be to press R to enter the Recovery Console or Enter to continue setting up Windows. Press Enter. A few more things will load. Maybe even a License Agreement screen. Press F8 there to accept. Then it will show you your current Windows installation and partitions on your hard drive. There should be some options listed to repair an existing installation, perform a new installation or delete or format a partition. Press R to repair your current installation. You will need your product key for this, so make sure you have it. It will go through and repair the Windows operating system on your PC leaving your data intact.

Hope this helps.