That's not good. The decimal should always be there. You most likely have memory corruption if the decimal point disappears suddenly. This is usually caused by flat batteries (if you see an L at the left side of the display, then your batteries are low). Once this happens, you usually need to clear all programming and totals and start again. If you want to attempt it yourself, you should get a service programming manual (not the same as the operating manual) and run through the readings and setup procedures. There is a Sharp ER-A320 manual here:
http://the-checkout-tech.com/estore/catalog/advanced_search_result.php?keywords=ER-A320%20programming&x=0&y=0
Once you have the manual, let me know and I can show you the sections you need to work through.
Mark
February 2010