You should be able to make the necessary account (password, profile picture and the welcome/logon screen is displayed or not) related changes through the User Accounts applet in the Control Panel.

Again, without knowing what you have done (installed) it is hard to say what caused the initial change (as I mentioned before .NET installation is a common cause -gotta love how MS surprises its users-) and also the tinkering your curious little hands have done...possibilities are....anyhow, glad things are back to normal with the reboot.

Hope this helped clarify things a bit.