Router has died. Need Advise Please.

[EddyCurrent]

Just to get this clear.
I have used CY 4 Core 1.5mm/2 cable from the VFD to the spindle, But I need to connect the screen to earth not just at the VFD but also at the spindle.

Yes

I will fit CY 4 Core 0.75mm/2 cable from the drivers to the stepper motors also the screen will be earthed at the driver end at a star end earth point and at the stepper motor end.

Yes

I will fit CY 2 Core 0.75mm/2 cable from the breakout board to the limit switches with the screen earthed at the breakout board, but the screen not connected at the switches.

Yes

I could use CY 4Core cable between the breakout board and the stepper motor drivers also the screen earthed at both ends.

Yes if the diameter is sensible to do so.

All ends will be joined to a common earth point in side the CNC control unit.

Yes, The idea is to ensure there are no voltage differences between any of the screens so a star point is the best way to achieve it.

Should I also run a earth cable between the control box and the CNC machine?

Yes the machine must be earthed for safety reasons.

Like I mentioned earlier if you subsequently have any problems related to this you can always disconnect one end of a screened cable to see if it improves.