Hi Tariq, The DSP is fairly straightforward to use - once you get the hang of it.
I hope you have NOT connected the DSP to your computer? This is what causes most of the problems.
When you turn the machine on - the DSP screen should light up and show a question " Go to Home? ". This is a command. Press the Home button and the gantry will go to the Home position. Nothing can happen until you do this.
To set the Origin position, you manually jog the gantry to your selected starting point (which should be top left of the table, but in about 20 - 30mm from the Home position. Mark the spot clearly with a pencil. ) . Short bursts of the buttons are required to get it to the precise point.When it is at the precise point - press X/Y-O button ( no.4 ) and it is set. Now press Home - gantry will return to Home position.
You should not need to set X/Y Zero anymore unless you change the starting point.
Have no idea why you are seeing the Z over limit. Z- takes the Spindle down toward the table to set Z Zero. Check the limit switch. Is it secure, or is the tab bent?
Hope you have not altered any settings. If so, the Pulse Equivalent Settings are X 127.3, Y 127.3, Z 400
But first, try the Home button and see what happens.