Re: Reformatting :
As a LAST result, yes. However unnecessary at this point.
To view the Event Logs, you need to right click your My Computer Icon.
You will see an option for "Manage".
Once the management console opens up, you will see the "Event View". Open that up and select the Application log.
By default it is arranged by date. Look for the source column. You should see the "userenv" under the source column. You can double click the entry to open it up. Please copy paste the contents of that log into this thread so I can take a look.
As for the User.Name.bak... Lets not worry about that quite yet.
Lets focus on why this is happening.