I have a Dell Studio 17 running Windows 7 64bit. It's been fine for years but a month or two ago I noticed that when I have an external monitor plugged in, if I try to use the built-in touchscreen all touches go to the external monitor. The touchscreen works fine when no external monitor is connected in both Win7 and Win8. (I have not tried it in Win8 with an external monitor.)
I also have a Mimo touchscreen USB monitor that works fine. Whether it is connected or not appears to have no influence on how the built-in monitor behaves.
I have looked at the touch settings in the Tablet PC Settings applet but can't seem to fix it there. The display options in that applet list all monitors. I select Mobile PC Display and tell it to calibrate, the calibration form comes up on the laptop display but when I touch it to calibrate all the touches go to the external monitor so calibration doesn't work.