Couple more things to try...
1. While in normal mode, before attempting shutdown, make sure all windows are closed. Then look at the icons is systray (next to the clock). Right click on first one, click "Exit". Try to shut down. If no joy, right click on next icon, click "Exit". Try to shut down, and so on.
If the above doesn't work
2. Try to get (borrow) PS/2 keyboard, and mouse, and plug them in instead of your USB mouse, and keyboard. See, if it'll solve your shutdown problem.