HeatherHaze
I have a similar problem with an M-Audio Oxygen 61 keyboard. I'm pretty sure it's the M-Audio drivers not playing nice somehow. It's a major pain in the derrière but I've chosen to simply deal with it so far. Would love to find a fix.
I am on my second Oxygen 61 (this one is 3rd gen, the first one which I wore out was 1G) and I have never had this problem. Drivers have been fine. The only "issue" I have ever had is on a rough stop (normally due to a flaky plugin), I have to wait for the MIDI display to disappear in the toolbar before I can stop bitbridge and SONARPDR.exe from task manager, which I believe is common for M-Audio Midi devices.
I checked my Power settings in Control Panel and am using "High Performance" which prevents the USB port from ever hibernating.
The only other suggestion that might be worth a try is to use a powered USB hub (with an AC adapter) as sometimes especially if you have a lot of USB devices the output power on a USB port maybe insufficient to properly power the device.