Hi Ronei, welcome to the forum. The latest OS version for Virus C is 6.5
You can download it from the original Access Music website (
http://www.virus.info/downloads )
If for some reason you are unable to do so, I've temporarily uploaded OS 6.5 (English version) for you
http://www.infekted.org/virus/files/...50x352_INT.zip
As for the knobs not working correctly, could be a couple of things:-
Firstly back up your patches as I'm unsure if this will reset them. Once you've done so, turn off the Virus. Then turn the Virus back on while holding down the LFO 'shape' button. This carries out a system reset. The manual mentions: "No data will be lost during this procedure, although some global system settings such as 'Global channel' will be reset".
If that doesn't work, the onboard knobs may simply be de-activated. Try this:-
Hit the CTRL or System edit buttons, then go through the menus (using the "Parameter" arrow keys) until you see:
1 MIDI
Panel = MIDI
Then use the Value arrow keys to make
Panel = Int+MIDI
'Int' stands for internal (meaning local control), so setting it 'Int
& MIDI' means you can use both the onboard knobs and external MIDI to change parameters.