Yes. If you have administrative rights to the computer, you can access other user's files. Windows does not encrypt user data by default. All you need to do is at the lock screen, hit Switch User and then log in with an account that has administrative privileges. Or if the computer is a member of a domain, you can access them over the network by going to \\PC-NAME\C$ where PC-NAME is the name of the computer.
Note that this is not a security violation in any way. You must already have an account with administrator rights on the computer in question. If you do not, then there is no way to access the user's data through Windows. You'd have to extract the user's hard drive to get at them.
As you said "break into the user's account" in your question, I am giving you the benefit of the doubt that you're doing something ethical (like maybe your English isn't so good?). But if you really mean to break into a computer that isn't yours to take files that don't belong to you, then this is not a hack site and you will not get assistance here.
I would advise you to reword your question.