I'm using the Dale LT544D plus for the first time on K machines. When I open the neutral I'm unable to power up the machine. Is there anyone using this tester who might have seen this?

In a 120Vac line you have Hot (black), Neutral (white), and Ground (green). Hot to neutral is your 120Vac. If you open the Neutral you will not have any power.

It is normal for it not to power up with the neutral open. If it does, your neutral is shorted to ground somewhere.

our biomed dept. always tests this for us. I am in the process of getting a leakage meter, can anyone elaborate on what you need/should be testing and explain it or lead me to lititure on it?

NFPA 99 goes into very great detail on electrical leakage and ground resistance. You'll probably have to check with your biomed department or your electricians.