OK so lets go down the check list...
1. Not the desktop service doing it
2. Not drivers doing it (Such as video) since it happens in safe mode as well and only the bare minimum of the drivers are loaded in safe mode.
3. Keyboard and mouse are good. Having you try completely different ones covered this.
From the sounds of your last post, it is now only notepad and notepad++ doing it, before you said other programs did it as well, but from the last post you said the others where not, correct?
Also does it happen if say you only open one? Say you only open notepad and not notepad ++. How does note pad do on its own? Does the problem seem to start only after you open notepad++?
Shane