Windows XP Service Pack 3 problem

I downloaded Service Pack 3 for XP and after it installed and I restarted my computer I was informed that some pieces of files could not be found that may be needed to run XP correctly and that I should put in the XP cd and reinstall but I don’t have the Windows XP cd to reinstall it and if I did I still wouldn’t know what to do because I am truly a novice when it comes to the computer.

This is not a notice that only happened the one time after installation, it happens every time the computer is turned on now.

Can anyone please tell me if there is something else I can do to get these files or pieces of files that seem to have vanished back?

Thank you very much and I really would appreciate any help.