I have a Leonardo board and was happily uploading sketches, no problem.
Then after one upload (I'm not sure it finished successfully) my leonardo now automatically disconnects from windows (win 7, 64 bit) after about 12 seconds. Too quickly for me to upload another sketch. The COM port comes up, but it's like the device itself crashes and takes down the USB connection with it. (Maybe having a seperate USB processor was a good thing afterall :)
There was nothing being printed out to the serial port in the sketch so I can't tell if that's working (nothing appears on the serial monitor)
The orange L LED glows up and down as normal after booting (about 10 seconds), then goes blank. A few seconds later the USB disconnects. The green ON LED stays on. Power is still being supplied down 5v etc (I have a gameduino attached, my code appears not to be executing, though it was the first time non-sample code was uploaded) Disconnecting everything from the board makes no difference (so it's not to do with the gameduino)
I've tried a couple of other USB ports on my machine, pressing reset just causes it to re-connect to windows... and disconnect again.
Does anyone know if there is something I can debug, some USB logs in windows? some way I can flash the arduino again? (maybe a command line tool might be faster with a very-blank pre-compiled sketch?)