I login to my windows xp2 and I got the isass.exe error and I tried fixing by repairing the windows xp and still got the same error,what should I do to repair this error?I'm using a hp laptop

Check and see if it's a worm or virus by installing malware bytes. Best program I've used thus far
For finding and eliminating worms, trojan horses, or other malware.

http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html

If lsass.exe is in any other
Directory besides C:\Windows\System32 it's malware and must be removed.