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Error and solution:

Well my MB tool after couple years of good use and many smiles suddenly is giving me some sadness.
All was working fine. Suddenly now when I plug it in then VVDI MB Tool software says ” CANNOT FIND DEVICE”.
I tried another USB cable, another USB port, Another Laptop with Win7. Nothing nothing nothing.
Doesn’t even show a port in Device manager. I then tried FTDI prog to see if that detects it and nothing……..

Detecting fault isn’t and easy task if you are not skilled with electronics (low level let’s call it), important thing for ftdi to work is to have supply 5v usually taken from usb (pin 20 vcc pin 19 reset), usb data lines D+D- to FTDI pins also should be check these go to pin 15 & 16, then RxD and TxD (pin1 & pin5) these should go to main MCU.
Check FTDI designs and see how VVDI Mercedes has done the configuration.
Check connections with multi meter (could be usb connector faulty), some designs have 22ohm on data lines D+ & D- and also a 1K resistor for reset FTDI during insertion on PC so device is detected properly.
Hope this helps a bit concerning FTDI check, since you said Mprog (ftprog) doesn’t detect the FTDI properly…, worst case could be faulty FDTI due some static discharge.
Check Attached schematic VCC,GND, RESET TxD & RxD are important for you (this is a example of using FTDI in some circuit).

Test updated:
Ok So atleast I got some smiles back. 
This machine does not have FTDI chip. I don’t know how it communicates… Maybe doesn’t need FTDI.
I measured voltages coming in from USB and on the closest compnent to the USB port I found that I had one pin with 5V and others nothing.
I opened up my VVDI2 and VVDI prog to compare and tested them and found that on the same component next to USB port I had one pin with 5v and other with 3v.
So I took the component from my VVDI prog as it’s the cheaper of the 2 to experiment with and moved it to my VVDI MB Tool and connected it up. Voila it works again. It appears in device manager and also software reads and everything working fine.
What component is it you may ask?
4 Pin SMD marked WR1. With some google searching, I find that it is PRTR5V0U2XESD Protection. Seems this is specifically designed to protect your device from any Surge from the USB port. This component acts like a fuse which will blow but prevent further damage caused by static / USB surge when connecting and disconnecting.
Cost of component is around $0.3 each or even less depends where you shop.

You have done well, STM32F4xx if I’m not wrong VVDI use and this MCU has USB witch can run as Virtual COM Port Host (CDC Host), USB HID etc.
For test purpose only when you had noticed the fault even with removed ESD protection the device should be detected properly, but mounting a new esd protection is highly recommended.