If you only changed the name and nothing else, that would not cause a logon issue unless you are part of a domain. How is the system setup and what exactly happens when you try to logon, error message, how you logon, etc...
As it is my office system, its in domain.
I tried to change the name of computer. it didn't allow me. But as I created a workgroup, it let me do dat. I got msg, plz reboot a system to apply changes. I restarted system.
Later,it is not letting me log into it.
I tried Domain\username, workgrp\username, but it failed.