Computer won't Sleep

The two are definitely associated. I booted into single-user mode and got several lines of text starting with "USBF:..." and including the text "MakeDevice error creating device", some ASCII that apparently identifies the device and, finally, the text "releasing device". There are three or four lines like this. I then typed "reboot" and, when the computer booted, the System Profiler couldn't see the hub in the Cinema Display (it can still see the keyboard and its hub) *but the computer will stay asleep*. That's right - the hub in the Cinema Display isn't available (the mouse doesn't work if plugged in there) but the computer will sleep as expected.

Next, I restarted normally (not via single-user mode) and, when the computer booted, the the System Profiler could now see the hub in the Cinema Display (the mouse worked when plugged in there too), *but the computer woke up immediately on being put to sleep*.

I'm sure I have a USB issue and it's _new_ - this same computer/OS used to sleep fine. I'm wondering if I've developed a hardware problem - how can I test for this?

Thanks in advance,
Steve = : ^ )