When the computer is powered up, the first user is able to sign in with his/her password. after that, the computer changes the user passwords. the next user must power down the computer and back up in order to sign in with the correct password. what is happening and how can I stop this? I teach high school and this only happens when using a Dell Optiplex 755. All of the other Dell's I have do not have this problem.1 person needs an answerI do too

Hi, It sounds a bit strange that the User Password changes automatically. It could be a handy work of a malicious application or virus. I would suggest you to follow the methods listed below: Method 1:Start the computer in Safe mode, and check if the issue persists. Please follow the steps mentioned in the link below to start the computer in safe mode:http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true If the issue does not persist in safe mode, perform clean boot to find the issue causing item. Refer to the link mentioned below to perform clean boot:http://support.microsoft.com/kb/310353 Method 2:Perform an online scan of the computer with Windows Live Onecare.http://onecare.live.com/site/en-us/center/whatsnew.htm Regards,Gaurav Prakash - Microsoft SupportVisit our Microsoft Answers Feedback Forum and let us know what you think.