You are experiencing problems booting into Windows XP in either Normal or Safe Mode, or encounter missing files during startup.
Repairing the bootability of a Windows system drive should be a lot easier than this, but at least the Recovery Console gives you access to some easy critical fixes to get you going again. Recovery Console may be the only way to regain the use of a Windows XP installation without having to reinstall the entire operating system. Beware that writing over the Master Boot Record will disable third-party boot manager/multiboot software that uses the MBR as a start and run point for the boot manager program, including multiboot features of Linux/Unix operating systems that offer different operating system choices to boot from.
An excellent step-by-step guide to the Recovery Console with screen shots of the process can be found at http://www.wown.com/j_helmig/wxprcons.htm, and a superb explanation of the options is available at http://www.kellys-korner-xp.com/win_xp_rec.htm.
An exceptional tool for restoring and fixing nearly all system problems is Barts PE disk. Downloads and documentation available at http://www.nu2.nu.