My tablet thinks it's communicating, but it's not. . .

I have a Wacom Graphire4 (CTE-440) tablet. I bought it off my sister a few months ago, after needing to buy a new pen (the pen works fine with the tablet). The tablet is probably three years old and hasn't had any major problems until recently.
So, lately, my tablet has been a pain getting the blue light on, it's taking a little longer than usual, but whenever I do manage to get the light on, it won't really work. I run my pen across the tablet, nothing happens on my moniter, yet the light still flashes green. It's the same thing with the mouse, whenever I click, it flashes green, but does nothing. It thinks it's comunicating to the computer, but it's really not. . .