I have a USB MOTU interface that works great most of the time.
 
Currently Sonar sees it and uses it... but Windows all of a sudden does not list it in the Playback Devices window. Therefore I cannot select it as the default sound source like I used to do.
 
I updated the drivers a month or so ago. Could that be why? I'm not sure if I can revert to the previous drivers but will try to locate them.

1.What device is it? I can help if its the MOTU Audio Express (which I use)
 
2.Is it showing in Device manager?
 
3.Try inserting it into an alternative USB port (sometimes Windows can get very confused with USB devices - If this is the case you'll need to flush out any dead USB devices from within Device manager by showing all disconnected devices as well as connected and you can delete any USB device that you dont use from there)
 

Hmmm...I use a Motu pre 4 Usb device...and the latest driver seems to not have output ports labeled right...in the windows control panel/speaker playback devices for me...(for setting win default playback and record in win 7)..it shows output 3/4 and 5/6...there is no 1/2, which has now become 5/6....and there should be no 5/6 output as it only has output 1&2 3&4, and 2 x phones
 
So yes the driver may be in need of addressing by the backers...I have made a ticket on Motu sight about My issue...if reinstalling the updated driver does not resolve the problem, perhaps reverting back to a older version may solve it..?
But do not stop there, make a ticket with Motu if it continues, and let them know...

MOTU Track16 here with no issues.

soens
I have a USB MOTU interface that works great most of the time.
 
Currently Sonar sees it and uses it... but Windows all of a sudden does not list it in the Playback Devices window. Therefore I cannot select it as the default sound source like I used to do.
 
I updated the drivers a month or so ago. Could that be why? I'm not sure if I can revert to the previous drivers but will try to locate them.

I would definitely try giving MOTU support a call. There may be some sort of update or troubleshooting process that they could take you through in order to see why this is happening. 
-DG

Thanks guys. Yup, Audio Express and I too have weird output labels with the new drivers. They don't seem to like Win7 too well. The unit worked great with WinXP.
 
I suspect the drivers or the HUB which seems to be the weakest link in the system. I've spent time with MOTU support before with another issue so back to the phones, I guess.
 

Roll back to the other drivers you had a month as that is the only thing that changed

Windows "hoards" all old USB drivers, unless they are cleaned up occasionally.  Over time, this can cause USB driver-related problems like you are experiencing.
 
Here's one fix:
 
http://www.symantec.com/connect/downloads/usb-device-cleanup