Not very clear what is happening. Exactly what default settings are you talking about? If you make changes to your settings, but don't reboot, some changes won't take hold if the system shuts down improperly like with a power outage.
Are you talking about your files? Are they no longer showing up on the Desktop or in My Documents? Are you logged on to the same account you get to when you check in the User's directory? You may have been logged on as a temporary account, Windows would have put up a message about an error loading your profile and using a temp one.
The Guest account is useless to do anything with.