[GTrumpet]

We bought an Mbox 3 and have been trying to use Pro Tools LE 8.0.5 on a two different Windows 7 64-bit systems since July.
Initially we installed on a laptop and it worked for a while, then we got the "Unable to locate Digidesign hardware" message. We tried everything we could find here, reinstalled a number of times, etc., then gave up and switched to a different, more powerful system (the first one was no slouch).
Once again, PTLE worked for a couple of weeks and then yielded the same error message again. So I tried everything I could find here and that made no difference.
We broke down and paid for a support call. The tech spent about 45 minutes going through everything, checking for the same stuff I had already fixed. Then he too gave up and issued an RMA for the Mbox 3.
I hope that fixes it.
He said that they did have a batch of bad hardware and he also said that some of the Mboxes were very sensitive to being unplugged from a USB port while the system was powered up - apparently doing so may damage the unit.