Start your computer once with the CD when asked. Then click 'Start I Run' and type the command 'SFC /SCANNOW' and press [Enter]. The SFC (System File Checker) will scan your system for corrupted or missing system files and replace them accordingly. At this time it will ask you to insert the Windows XP CD in your optical drive. When all is done, restart the system arid check if the problem is solved.
Alternatively, you can also update your Windows XP to the latest service pack (SP3) to get rid of the problem. Also check your system for possible malware and viruses.