Mark248:
This is the circuit, i am using 48V on the input but then using voltage divider too,
ignore the other blank resistors as i have to make 2 other circuits to compare too, but as you can see comparator is not showing anything
They make sure the output of the divider is at least 1.5V below the LM339 supply voltage at all times.
You have forgotten the pull-up resistor to 5V on the output.