It has been working fine and then one day it does not receive any signal. The MIDI activity lights don't light up. I updated the M-Audio Fast track Pro driver. The M-Audio and the sound max are both listed as input/ outputs. What am I missing?

Thanks for help!

? USB problem

Try a different socket, check to be sure your USB ports are working in device manager, and that you do not have power saving settings enabled.

when this happens the worst thing in my opinion is to start scampering around changing things.
sonar doesn't just magically change settings. so before you start changing all kinds of things look closer to home.
don't jump the gun, its either a windows update, (plugin in the wrong usb port)
yes like the user above mentioned. your device will work, but flakey.

After you updated your drivers, you probably just need to reconfigure the MIDI settings and ins and outs. Its nothing bro.

CJ

In my case, Sonar DOES randomly change the Ins/Outs of tracks which in turn can make it stop seeing MIDI.

For example, a track may be set-up with input as OMNI and output as MIDISPORT Port C.  One day I will open the project and input/output will be something random like Fantom and ARX.

Something similar happens with audio as well.  One day the audio In may change from Channels 3-4 of the V-Studio IO to 1-2 or to Fantom, or to something else.

Sweetwater thinks this is a bug with the V-Studio IO.  While they may be right, I know of no other V-Studio user with this issue.  I think it is something flakey in how Sonar was set-up. 
If it is the IO, I would be inclined to think it is a bug in the integrated Fantom since the set-up and support of the Fantom have always been weird.  That was a selling point for me in getting the V-Studio, but it has been a pain from day one.
Just throwing this in on the chance it relates to this post.

I have seen this when Windows is allowed to turn off USB devices for inactivity.  This can be changed in the power settings, to disable that feature of Windows.

As for anyone with inputs changing, I think that is possibly due to removal of a synth in the synth rack - but there may be other causes I am not aware of.

Bob Bone

I have seen this happen when disabling the onboard sound via Msconfig > Services.

You must not disable Windows Audio or Windows Audio Endpoint Builder

For some reason Midi requires both of these to be running.

Depending on your input device (i.e. keyboard), could you have accidentally bumped into the switch or knob that changes it midi channel assignment?