pirates9_9

Hi I have a problem with the login screen of my xp machine. Here is the scenario: I lock my machine using win+L or switch user then sometimes it wont log me in, even if I enter the correct passowrd it will say wrong password. I donn have a password for guest account but when it dies it also asks for a password of Guest account. But when I reboot the machine password is accepted. Can sum1 tell me what sthe problem with my machine ?? --jack