It does sound like you acidentally logged into the wrong account actually.
We get the "preparing your desktop" thing when logging into our network if we've never used that machine before. Its generally just copying your user settings over the nextwork.
You could presumably check this by checking the different user profiles on your machine. See if there are any others than your's
Run system file check and let us know the result SFC /SCANNOW Command - System File Checker