I've had the same issue, on two different systems. Touch screen will stop working, going into the control panel to configure the touchscreen basically tells me that this is not a touch-enabled PC.
Happens when the system is left alone for a while (overnight usually - sleep is disabled, but the monitor will shut off). Also happens when switching users. Just got done with Dell support doing a remote session on my system, and they did something that I would have never expected - they installed an HP driver. Of course the tech claimed that it was a "generic driver" but it definitely said "Verified Publisher - Hewlett Packard Corporation". File is sp45210.exe (still on my PC) if anyone is interested in looking it up. My guess is that this is a driver issue with whomever provided the touchscreen (Based on new hardware in device manager, it's Wacom) and HP fixed it first, and Dell is issuing this patch subtly to fix the issue.
It's only been about 15 minutes since they applied it, so I'll touch back in the morning and tomorrow night to report if it appears to be fixed.