What is the event id in Event Viewer for lock, unlock for a computer in Windows XP, Windows 7, Windows Vista and Windows Server 2008?
The lock event ID is 4800, and the unlock is 4801. You can find them in the Security logs. You probably have to activate their auditing using Local Security Policy (secpol.msc, Local Security Settings in Windows XP) -> Local Policies -> Audit Policy. For Windows 10 see the picture below.
Look in Description of security events in Windows 7 and in Windows Server 2008 R2 under Subcategory: Other Logon/Logoff Events.