I'm getting a delay when entering my password at the log on screen in Windows 7. What I mean is that I can select the text box but pressing keys does nothing. I had this problem initially on this computer with Vista installed - when I reformatted and installed Windows 7 the problem went away - but over the weeks it is slowly coming back (the delay seems to be getting longer).

Any clues as to why this is happening and how I can fix it? It currently takes about 4-8 seconds before it will accept keyboard input.