It's a bit difficult to understand your question.
In order to install W7, you will need to boot from the CD/DVD.
In order to do that you will need to change the settings in the BIOS. If you can access the BIOS as you say, than you should be able to change the boot priority in order to boot from the W7 media. You should also find in the BIOS a setting to enable support for USB keyboard and mouse.
Once you boot from the W7 media, yu will have the option to delete the existing partition, format and install W7.
You don't need to format the C drive, prior to starting the install process (in fact you won't be able to format it from within Windows - as this would be akin to asking the OS to commit suicide)