If it's only showing 200-400 psi at room temperature, the tank is running on fumes at this point. Literally... the liquid CO2 has all evaporated and only gas is left, at a much lower pressure. So this would read quite low when the tank is chilled.
With gaseous CO2, the reading won't change significantly based on temperature. If it's reading 300 psi at 77°F, it will drop to 275 psi at 32°F.
Jeff, were you testing it in the store using his personal tank? Based on what he's seeing at home, it seems like he's simply out of gas.
Testing meaning we put his regular on his tank, yes. LHBS doesnt have a gas setup(is it odd that they dont?) so there are no tools to check the tanks. we put his regulator on and the guage was hovering right near the red. It never occured to me that going in to the red of the guage would mean all the liquid co2 is gone and its only gas under pressure. it makes sense now that Navin and the others said something.
Is there anything else it could be while we are at it?