At this time, I really suggest you install Windows over your ‘old’ installation.
You won’t lose your programs and settings neither your data.
Install Windows from the CDRom. Just choose ‘Repair’ installation of Windows and install ‘over’ the old installation.
This is called overinstallation and it can solve the problem and you won’t lose your programs, settings, data, files, etc.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;315341
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q314058
http://www.webtree.ca/windowsxp/repair_xp.htm