Go to run, type: cmd

In the prompt type: at (specify time in military format when you want the new command prompt to appear) /interactive cmd.exe

Type: at

Wait a minute for the time you specified in step 2 to come around

Close the old prompt

Open the task manager

End the process: explorer.exe

Close manager and type in new prompt: explorer

SYSTEM user is now accessed. You can close the prompt if you want now

To end this, simply go to the task manager and end the process: explorer.exe again.

Close it and then go to the task manager again

Go to new task in the file drop down menu and type: explorer

You will now be logged back in to your previous username. You will have to put your original wallpaper back on though I think.