Hallo Mahmood,

now situation gets clearer.

It's not the first time, that the absence of motor filters (snubbers) causes lots of trouble!
You told, that sometimes a driver breaks within normal operation. This could be caused by the case, that more than one motor is working at the same time.

If you really have varistors from mains voltage terminal to protection earth terminal in each monitor, then every overvoltage spike coming from a motor is coupled directly into the cable shield!
This could indeed be the mechanism of failure!!! Is it legal to have these varistors connected to protection earth, by the way?

The bad thing with protection earth wiring is not so the static resistance, but more the existence of relevant inductivity. Then, even small overvoltages can heaviliy increase, caused by the resonating of wiring inductivity in combination with stray capacitance (also mains filter capacitors).

1. So, you should insert motor filters (snubbers).
2. You should take care, that these many monitors are not all together powered-on at the same moment.
3. And you should add surge protection circuitry to the vga drivers.

Unfortunately, I'm not familiar with AC motors working with starting capacitors. May be they suffer from very high inrush currents?? Could an inrush current limiter be added??

To the surge filter:
In any case you must add something showing very low junction capacitance. Something like very low capacitance transzorbs are essential. Althoug some nanoseconds slowlier than standard typs they are fast enough to handle your surges.
But unfortunately, transzorb is not enough, because nevertheless a certain overvoltage can be existant at vga pin, for an unsane period of time. So, I would also add BAT54 diodes (or similar) directly from vga driver pin to Vcc and 0V. If your driver works as voltage generator, this obligatory 75Ohm resistance could then limit the resulting current.
Again, from vga pin to monitor: First the two BAT54 from pin to supply rails. Then this obligatory 75Ohm resistance. Then the low capacitance transzorb from the line to 0V. This transzorb should be located as near as possible to connector. And keep in mind, that low capacitance parts here is really essential, otherwise signal transmission will suffer.

Hope this helps,
Kai