Trying to cover across the board here...

Update chipset drivers (Intel driver update or AMD equivalent).
Update the audio interface firmware if possible.
Update the motherboard BIOS.
If it's a FireWire card check for latest firmware.
Windows update.
Is there a way of resetting the hardware? (Not sure about this interface)...
Have a go at renaming AUD.INI

Cheers..

My starting point would be renaming Aud.ini and allowing Sonar to rebuild that. I did notice that Windows (7) ran some sort of huge update on both my systems recently with at least one if not two reboots before it was applied which may or may not be relevant. Having said that I run a FW interface (not MOTU) which hasn't been affected.

FastBikerBoy
I did notice that Windows (7) ran some sort of huge update on both my systems recently with at least one if not two reboots before it was applied which may or may not be relevant. 

I don't know if it's my imagination or not, but it does seem the number of reports of weird behavior increases after Windows updates. 

I sincerely doubt that it is the Motu unit itself - if it's speaking at all via some audio method, then it should work for all. The differentiation in access methods for applications happens within the PC, not at the unit or its hardware protocol.

Most likely, there's either some corruption or confusion within the registry concerning installed drivers. It might be worth it to see if you access ASIO via USB for diagnostic purposes. Normally, reinstalling the driver should work unless there is some serious thrash/misconfiguration in the registry setting for the driver.

I tried deleting and rebuilding the AUD.ini, no change.  ASIO driver mode has no I/O to report in the Driver settings and the devices tab.
 
super G - as I said above, it doesn't work in USB mode at all now.  when I plug it in to USB, even with the power adapter plugged in, it doesn't even boot up.  the screen is blank (but the backlight is on).  if I plug it into firewire, it does boot up, but no longer works in ASIO mode in Sonar.
 
alex - I did reinstall the latest MOTU drivers, but I haven't updated the firmware yet, I'll try that.  I haven't done the bios on the motherboard in a quite a while, I might try that as well.  I do not want the latest firewire drivers, I'd rather stick with the legacy which have not changed in several years.
I might be able to reset the hardware, but I assume it will reset anyway when I update the firmware.
 
Craig - yeah, I'm probably also going to roll back the last updates and see what happens.  something funny is happening with my IE, also, the security settings changed with this last update which wouldn't let me download anything and I had to go reset the security settings. 

unbelievable!  it was something in the last MS "critical security" update that caused the problem!!!  once I restored the computer back 2 updates ago (I got 2 updates yesterday, one in the morning on one in the afternoon), I started sonar and now the MOTU is working correctly again. 
 
thanks everyone for your help!

Wow! I am really sorry that an update put you through this!

yeah, that was weird!  thanks John

Good news!
 
That's why I keep my DAW offline... I don't need security updates.
 
People say it's ok to put your DAW online.
 
I say that people that say that don't have your best interests in mind and are just rationalizing placing their own music making at risk and trying to get everyone else to agree so it doesn't seem so obvious that it was going to happen when, not if, it happens.
 
Heck, my backup DAW, circa 2005, works just as good as the day I bought it. It runs XP and has a lower real life round trip latency than my current Win7 SuperDAW, because I never updated to MOTUs more recent drivers or Windows 1394 updates. Neither have ever been online since I've owned them. It keeps me happy. :-)
 
Glad you got it figured out.
 
 

Yeah, I agree it is best to keep the DAW offline. But I don't use mine for professional recording, and it has to be a multipurpose computer. In this case, that really big me in the rear, tho!