My PC will not boot up. It doesn't even get to Windows booting. A blue screen pops up and says "Windows has detected a problem on your pc and has been shut down." I cannot get past that. I do not have any type of software to format my PC. I would like to just format all of C: and start over with Windows XP, which, I do have. Any ideas?

You can do 1 of 2 things here

-do a repair installation that will more than likely resolve your issue
Repair Installation
A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied.
Perform a Repair Installation

Or

-Do the format and reinstall from scratch
How to Format Drive and Install Windows from Scratch
Geek to Live: How to format your hard drive and install Windows XP from scratch

Another thing you can do if that doesn't work is to write down the error code that the blue screen has (begins with 0x0000 typically), and do a Google search for that error code. Most of the time you should be able to find something that tells you what the error means and what can be done to fix it.