Do NOT reformat and reinstall as you will lose all your current programs and data.
In general you want to do a repair install and NOT use the repair console.
Detailed instructions for a repair install are here http://michaelstevenstech.com/XPrepairinstall.htm He also describes how to create an XP disk with the service pack included easily.
If you can no longer do a repair install or find it too complicated, DO NOT reformat and reinstall as this will wipe you out and leave you with nothing but the operating system. You would have to reinstall all your programs and much of your data would be inaccessible.
Reimage can repair your system even if a repair effort fails. It costs a little but it is well worth it to save your data. It takes about 30 minutes and preserves your programs and data. If you are not happy with the results, you don't have to pay and you can reverse any changes that it made. It's good for a year, there's 24/7 tech support and it repairs XP, Vista and Windows 7 too. More information here http://www.askthecomputerdoc.com/blog/reimage-repair/