I"m having trouble with my tablet that I have had and used many times before. It's supposed to have 1,024 levels of sensitivity, but now, when I'm in my brushes panel, and I try to control the brush size by pen sensitivity, it comes up with the little orange error sign that says I don't have a pressure sensitive tablet. I have used it with this computer and with another that both have photoshop, but it's not working all of the sudden. I have tried googling it and updating to the latest driver for my tablet and downloading the latest photoshop update, but nothing is working. I have Windows 7 and the whole Creative Cloud on the Student One Year plan.
First check and see if Wacom has a driver update.
If their most recent driver does not solve the problem, then you need to call Wacom and work with them to see why the driver is not working on your system.