My suspition is that someone DID NOT hack into your computer.
First of all, there are reasons why windows will revert back to the classic theme (it sounds like thats what your describing). Most often this happens because your graphics card is not good enough to handle the aero theme.
You also mentioned another user account called "ASP.Net Machine Acct". That account is created by .NET. I don't know why, but I do know that it is not a threat.