Hey man! My first thought was that you need to update adb but I see you've already done that. Assuming you're not having any driver issues, I want to say that the phone needs to be in charge only mode (not mass storage).
Now if that simple change doesn't help anything, and you're on the updated adb, it has to be a driver issue, cable issue or issue with some other software running on the computer.
HTC sync for example can interfere with fastboot/adb. Even if your drivers are okay.
Also, since jellybean; with the updated adb, there is an on-screen prompt as a newer security feature.
So make sure your screen is awake and check to see that you aren't getting a prompt to allow your computer to communicate with the device via adb.