Touch screen issue

Have a client with a Dell 15" touch screen. It was working just fine until a few days ago and now all of a sudden its gone crazy. When you touch it the mouse is no where near your finger. I have recalibrated it numerous times, both four point and two point. I have the latest touchware drivers. I have done a linearization also. Sometime a calibration fixes it sometimes not. I can continue to do calibrations and eventually it will take and work flawlessly. Problem is after an hour, 5 hours 1/2 day, 2 days or whatever it chooses it goes back to acting up. Just randomly chooses how long it wants to work. I'm thinking video card in the PC. PC is brand new Optiplex with onboard video and 2GB ram. Anyone every seen something like this.