Hi @fisherofbags ,
Check that the touchscreen has not been accidentally disabled in BIOS.
To enter BIOS shutdown the laptop in the normal manner and then restart it and press the F2 key immediately after the laptop starts.
Once in BIOS go to Table 8 System Setup Options - Display Menu > Touchscreen and check that it is enabled. According to the service manual (see p.61) the touchscreen will always work in BIOS irrespective of this setting.
If it isn’t disabled and it works OK in BIOS, check the touchscreen in Device Manager (not sure where it is located but maybe check in Device Manager > Human Interface Devices or > Mice and other pointing devices to check that it is installed OK by the OS.
Not sure that it would be a loose cable as it appears that there is only the display cable between the motherboard and the display so I think that the touchscreen wires would be in it and it would be unusual for only the touchscreen to be affected and not some parts of the screen as well.
The manual shows how to gain access to the display and the touchpad so hopefully this is of some help.