Hallo Mahmood,

as Michael Neary already stated, cable capacitance is not an issue, here. If you work with impedance matching, means if source impedance of video driver equals characteristic impedance of cable and also input impedance of load, then cable capacitance does not play a role. Remember that with video signal transmission we leave the region of electrostatics and enter electrodynamics: An electromagnetic wave is travelling through the cable!
Cable capacitance only becomes relevant again, when heavy impedance mismatching is done for any reason. Then cables loses transmission line properties and can behave like a pur capacitive load or an inductive one (depends on typus of mismatch).

I'm not familiar with your vga driver chip, but I could imagine, that outputs see a much too low load impedance. This could be the reason for damage.
If you have a look into a databook of video amplifiers (MAXIM has very nice ones, in GeSi technology!), then you will notice, that a typical output can only drive a very certain number of typical video loads. If this number is overranged, destruction can occur. This means, that you can not connect an arbitrary number of monitors to one cable driver! If you want to connect a certain number of monitors, you must add some more cable drivers. And: Each cable must see the correct source impedance, which must equal the characteristic impedance of cable!

Let's have an example:
Assume you work with cable drivers, which are capable of driving of two typical video loads (75Ohm) maximum, then your circuit should look like this (driver assumed having voltage output!):



This circuit allows you also to drive only one cable, if wanted. Still then, the remaining cable is terminated properly.
If you want to drive 4 cables, two of such drivers are needed.

You statetd in one of your posts, that 22Ohm impedances are used. Well, for me this seems to be a violation of impedance matching!

To the ESD protection:
It's very easy to protect the video lines by the help of suited Schottky diodes! The BAT54 is very often used. In the following link you will find a typical application:

http://www.chrontel.com/pdf/an51.pdf

I think Michael Karas has also published a protection circuit using these diodes, here, some time ago. Advantage of Schottky diodes is, that much lower junction capacitance is introduced to the line, than compared with standard transzorbs. This is important, because relevant capacitances can influence the cable termination, which can result in an eroding of characteristic impedance matching.

ESD is mainly a problem, if you connect and disconnect the cables. But if cables remain connected, it's hard to believe that ESD events are causing the damage of your vga driver! Even if interference is coupled into systems via mains voltage, there is always the ground connection between the monitors and computer present, via the (shielded) cables. So, to me ESD events don't seem to cause the damage of your vga driver.

You asked, whether using of different phases of mains voltage for monitors and computer can badly influence reliability. Well, if there's a proper routing of Neutral in your building and no big currents are flowing along Neutral connections, I don't see a bad influence. But difficulties can arise, if computer and monitors get their mains voltage from separated mains voltage systems with separated Neutrals, and if high currents flow between these individual Neutrals. If this is the case, you should take measures, that all monitors and the computer with vga driver are supplied by the same mains voltage. And: Guarantee, that there will not be any high currents of motors and such stuff flowing through this connection!!! Route the vga cables and the mains voltage cables to the monitors in such a way, that no big ground loops are formed.

By the way, you told, that you don't have protection earth in your building. What are you connecting protection earth of computer and monitors to, then?

Conluding: I think your vga driver is damaged, because driver outputs are overrated by having connected too many monitors.

Kai