Can you look at the chip on the Atmega32u2? I have a similar device and it runs at 16mhz. So if you try to flash with an 8mhz .hex file it won't boot. I flashed this version of psgroove to mine and it works fine psgroove_teensy_at90usb162_16Mhz
EDIT: To get my software to work you have to install the driver, I use the Flip 3.4.2 software. Search for the driver in the flips program directory.