I have a Dell Latitude D620 with Windows XP. When it attempts to boot XP just continues to recycle without doing so. Nothing I have attempted to do in the BIOS has been effective.
Is there a way to access the C: prompt or reformat the hard drive so I can install software of my own?

If you want to wipe the drive clean and install a new OS, simply configure the BIOS settings to make your CD/DVD drive have the #1 boot priority.

Then, when you boot your computer, make sure that you have the OS media in the optical drive. The computer will boot from this media and during the installation of the OS, you will be able to configure the partition(s) and format the drive.