My first question is "what has changed".
(My second is "Did you remember to pay the roadie?")
I assume you are connecting directly to the PC and not through as USB hub.
Have you tried it with a PC that has a different OS.
Ideally XP with SP 2 or 3
Check the physical position of the USB pins inside the socket on the FanX.
Have a look and make sure they are clean, evenly spaced and not damaged.
Does it change if you move the plug about in the socket?
Like any socket it can develop problems with its connection to the printed circuit board inside the FanX, but as it has a mounting screw through the case close by it is less likely.
As far as a virus is concerned it is unlikely as it would have had to have been written specifically for the FanX and unless you are enriching uranium with your synth and you live in Ir... ah sorry.
It really feels like it is connector related FanX PCB->socket ->Plug -> cable -> Plug -> socket PC
Try and find someone that has a working PC/FanX system that will let you try your synth.
If it works then you can rule in/out your synth & cable. - I'm in Melbourne Australia
All the best