How to format windows 7 without cd

without cd you can't
you can download linux cd and boot from it, and then format the hd with the linux's installer tools

Bootable USB?
http://emea.microsoftstore.com/UK/en-GB/Service-Centre/...
Use a Windows ISO or Ubuntu

Go to the command prompt and type "Format C:".You must be in elevated mode.

Make a bootable USB drive.

If the USB drive is big enough you can also place the windows install files and necessary commands needed.