Administrator account's settings suddenly changed, looks like a guest account...?

Go to user accounts from the Control Panel and edit the settings there. Then create a password to prevent other users from accessing the administrator account.

Occasionally Windows XP makes a mistake and doesn't recognize you as an existing account, so it makes a new profile and you start out all over again.To check this out, go to your C:\Documents and Settings folder and see if you see more than one folder with your username on it. If you do, one of them should be your old profile with all your documents and favourites in it.It is rare, and I haven't found a proper solution yet. I've fixed it once, but the solution wouldn't work when it happened on another computer. My advice is to try logging in using a different admin account if you have it, delete the newly created profile folder (then one without your old docs in it) and try logging in. If it doesn't work, it'll just create the same folder again. If that happens, just transfer all your docs from your old profile (eg. my docs, favourites, desktop) to your new profile and start again. Unfortunately it doesn't save your program settings, which you would have to redo, like Outlook email accounts, desktop background, etc