For what it's worth, I have the same problem with an HP 250 G1, which also has a Synaptics touchpad, possibly the same part.
The touchpad works fine for 10-20 minutes, then suddenly only the top-left corner moves the pointer and the other five sixths of the touchpad are an enormous scrolling area, as if the scrolling edges suddenly got much wider.
(Try on your Toshiba to use the square inch in the top-left corner of your touchpad. You might still be able to move the mouse pointer, as I can.)
I updated the driver to version 16.5.5.1 (dated 4-Jun-2013) but I still have the same symptoms.
Also worth noting is that exactly the same problem occurs when I'm running Linux (Ubuntu 14.04) on the same machine. So it's probably not a driver problem (since the Windows and Linux drivers are different) but something in the hardware or firmware.
No later driver is available from HP.
The only (partial) solution I've found is to work around the problem by suspending the laptop and then waking it again. That sems to reset the touchpad somehow so that it works again for a while.
In Linux I can restart the mouse driver from the command-line to get the touchpad working properly again.
Code:
sudo modprobe -r psmouse
sudo modprobe psmouse
I can't find an equivalent Windows command-line trick that works reliably.
and then restarting C:\Program Files\Synaptics\SynTP\SynTPEnh.exe sometimes solves it, sometimes not.
My long-term workaround is to use a mouse instead and sometimes to disable the touchpad entirely