Several users have discovered that their touchscreen stops working from time to time, typically after waking from sleep/hibernation. If you experience this problem, you should run the Dell's touch panel firmware update specific to your display type (FHD or QHD+). This update also improves the trackpad responsiveness, particularly with two-finger scrolling (Synaptics makes both the touchscreen and touchpad used in this system).
WARNING: Thus far there have been 3 reports that the firmware update caused the touchscreen function to be bricked entirely (the display itself was unaffected). Those owners had to set up a service appointment with Dell to get a replacement display. Therefore if you don't care about your touchscreen and feel your touchpad is just fine, you may wish to avoid the update. Otherwise, accept the risk that your touchscren may not work after the update and require a replacement display from Dell.
In November 2013, before Dell released the firmware update indicated above, jphughan on NotebookReview's user forum suggested disabling the sleep mode for the touchscreen specifically in order to address the spontaneous unresponsiveness issue. If for whatever reason this is an approach you'd like to take, go into Device Manager, select Human Interface Devices, and look for USB Input Device (rather than the device specifically listed as a touchscreen, ironically enough). Go to the Power Management tab and uncheck the sleep option for this device. Be sure to monitor battery usage, as this theoretically means that the touchscreen will continuously draw on battery even when it is not being used.