Which OS version? Which tablet driver version?
Do the following:
1. Bring up System Preferences.
2. Click the Wacom Tablet pane.
3. At bottom of pane, click the About button.
4. A sheet is presented.
5. Click the Diagnose... button.
7. Another sheet is presented.
The Diagnose sheet should show version info, which you should post. If you don't see an About or Diagnose button, then find your software version info some other way.
The Diagnose sheet will continuously show real-time info about the pointing device in use, such as proximity, position, etc. If your pen shows proximity but no switches or pressure, then double-check your pen settings. If it doesn't show proximity, even when placed on the tablet, then you may have a defective pen.
Does your tablet's mouse exhibit the same problems as the pen? If so, your tablet may be defective.
Do you have anything metallic on top of your tablet's surface?
You should be able to determine more by yourself using the Diagnose sheet.
