How to Solve Unable to Log Into Windows XP PC Despite The User Name and Password Are Correct

Problem: On local area network (LAN), other PC (Windows Vista, 7 and 8) are not able to log into Windows XP PC with the correct user name and password.

Solution: the date and time of Windows XP PC are incorrect, re-set them.

source: https://superuser.com/questions/287009/logon-failure-unknown-username-or-bad-password-when-connecting-windows-7-pc-to-w