I have seen the touch screen fail, but lets try a quick test and maybe cycling it through this test will reset it. Do you have other terminals?
Power it off, hold the round button at lower right, then power it back on. Hold the button a little longer then release it. a keyboard should come up which allows the entry of 1287 if possible, enter this number then select LCD, then Touch Test. If you don't get any farther than the 1st step, then the touch must have failed. I have a NIB available at(###) ###-#### ***** lets try this first.
Round button? I don't have a round button.
OK, I am thinking along lines of a 2000, you said Sam4 but there is a model number..... Sam4 is the MFG. Anyway the manual should lead you to a diagnostics called "Touch Test". When there they have you draw on the screen to test the touch. Do that, get as far as you can then come out of diagnostics and return to the register mode to see if the prob went away.
What is the model?
530 ft I think maybe 520
I can't tell by your answer if you tried the diagnostics....