Enable Windows Task Manager when Disabled by a VirusOpen Group Editor Policy by Clicking on Start, then click Run and type in gpedit.msc and press OK. Once in the Group Policy Editor, expand in turn: User Configuration > Administrative Templates > System > Ctrl+Alt+Del Options On clicking Ctrl+Alt+Del You will have four option on right hand side. Double click on Remove Task Manager to change its setting: Click on Not Configured and then OK and Task Manager is available once again.
Some user can't login / The sign-in method you're trying to use isn't allowed. For more info, contact your network administrator.Open Local Security Policy by Clicking on Start, then click Run and type in secpol.msc and press OK.
Once in the Local Security Policy, expand in turn: Local Policies > User Rights Assignment
on clicking "Deny log on locally" on right hand side, make sure your user not here, if here just remove it and problem should solve. if the problem user account name not here,
on clicking "Allow log on locally" on right hand side, add the user allow log on locally.