Pressure Sensitivity Shorting Out

Hi.

My tablet usually works fine, but occasionally, the pressure sensitivity disappears for no obvious reason. This used to be a rare occurrence, but now it does it quite often. It will work fine for one brushstroke, lose all pressure for the next, and usually come back after a few experimental scribbles, only to fail again seconds later.

I've tried replacing the battery and had no luck.
Anyone know what I can do to fix this? Thanks a lot for your help.

- Emily


Ps: The program I usually draw in is Photoshop 2.0, if that's at all relevant.