As per the electrical diagram available in the Oscar manual here - http://www.nuovadistribution.com/oscar.html
, you have two wires leading to the water reservoir. One is most definitely a ground, the other leads to the control box. When the control box senses no continuity, it probably
shuts the machine down.
Turn the machine off and unplug it. Now temporarily
connect the two wires leading to the reservoir together and see if the machine will power up.