@Venom_ace
Dear Brother,
Firstly congratulations, Its really nice that you have shared your experience. I know its like a disappointment in the first place because of facing all this, thus I have decided to help you in detail.
I have recently bought the same car, and for the benefit of general public on this forum, let me share you what is the solution of your problems.
problem 1: Electronic system failure, in this scenario you must be feeling like your power steering, indicators, a/c, etc are down, breaks become very very hard but headlights keep working, and "Ignition" light turns on, even the engine is started.
solution 1: your car is a full electronic master piece, I feel like your CNG technician have powered your CNG kit by connecting its wire with ignition wire which is turned on when you switch on "ACC" via your key. FYI its in your KEY assembly, below your steering. The solution is that instead of powering up CNG kit from ignition wire, the mechanic should extend that wire and take it to left side till switch box, there you should find an appropriate fuse to power your CNG kit. Make sure the current received from fuse is not always on, but turns on when you move your key to ignition position. The fuses found in vitz are smaller in size to conventional ones, so tell him that he'll have to forcibly push it inside and lock it somehow. I am confident that this will resolve your problem.
problem 2: More over when i drive it on CNg the petrol tuning goes badly out and then car cannot run on petrol The mechanics say this model can run only on 1 option CNG OR PETROL
solution 2: for your information and for help of the general members of this club, the new vitz has a 5th generation EPROM (erasable programmable read only memory), something we have in computer and we usually call ROM/BIOS. If there is any problem, the system starts mall function and it keeps malfunctioning unless you do a "hard reset".
Do exactly as stated below:
To do a hard reset, put your key and take it to switch position (not ignition). now goto your battery, and open the negative terminal and disconnect it from your battery.
wait for 30 seconds.
touch the terminal with the terminal of the battery for 1 second and remove it.
touch the terminal with the terminal of the battery for 2 second and remove it.
wait for 30 seconds.
now go back to drivers seat and take the key to lock position, do not remove the key. (make sure you dont lock out the car 
)
now go back to terminal and do these steps:
touch the terminal with the terminal of the battery for 1 second and remove it.
touch the terminal with the terminal of the battery for 2 second and remove it.
wait for 30 seconds.
touch the terminal with the terminal of the battery for 1 second and remove it.
you've successfully completed a hard reset.
now connect the negative terminal back and you'd be able to enjoy perfectly both on CNG and Patrol, and dont forget to slap the mechanic who said "The mechanics say this model can run only on 1 option CNG OR PETROL"
I have one suggestion for you, If you want to get optimum pick on CNG make sure that your air exhaust/inh is trimmed to have with the help of white paper tape, i.e. its usually of this shape ( ), you need to cover half of it and leave half open ( | ) (i.e. left half covered)
Your first problem was that your RPM was getting down on CNG, I cant tell you if that was because of the hard reset, but if its still not resolved you'll need to play with mixer in your cng kit.
Regarding your dvd thing, I have no idea, so i'll leave that with other members of the forum
If you need to talk to me just in case, do send me a message on forum and i'll give you my number.
HTH
