check your power lead ground. if it's been snapped off or you have a bad plug, your static build up can cause all sorts of random issues when you touch it. might not be an issue all the time, but if you have started having especially dry days, it can become an issue.
the power supply could be failing as well. the screen runs off of +12v directly from the power supply, if this voltage has started going low, the overlay can do weird things like pulling the voltage down so low that the +12 used for the CPU gets spikes,dips and other nasties going through to the CPU.
i've seen something a weird as buzzing fluorescent lights causing crashes. your body becomes a giant antenna when you touch the screen so any stray fields can be plotzed into the machine. so the big magnetic/electric field you transmit through the machine from failing fluorescent light ballasts when you touch it can cause this too.
it's a matter of finding out what's changed since it last worked. if nothing has changed, i'd look into reloading the software (since it's free to do that) and if it's still does it...replacing the power supply. it's probably due anyways if it's original to the machine.