Windows xp start up

Hello,
· Were there any changes made on the computer prior to the issue?
· Which is the service pack installed on the computer?
· Do you receive any error code with error message?

1. Check the behavior by booting the computer in clean boot state. You may refer the below link on how to configure Windows XP to start in a "clean boot" state: http://support.microsoft.com/kb/310353
If the issue does not persist you may continue with step 2 from the above link.
Make sure you reset the computer to normal mode after the troubleshooting completes. Refer the section “Steps to configure Windows to use a Normal startup state”
2. Run online virus scan and check if any malware or virus activity found on the computer. You may run online virus scan from the below link: http://www.microsoft.com/security/scanner/en-us/default...

NOTE: Make sure you select the correct version of the operating system before downloading the scanner)