This is exactly what happened to me yesterday! I seem to have flashed a bad recovery after I finally decided to unlock the BL after much deliberation and lusting for some Kitkat goodness. Now it won't turn on. BUT:
It WILL give me a red LED (steady) when I do the Power + Vol-Up dance while connected to USB. However, the computer won't recognize it since it won't turn on at all. No SUS, no EMMA, no nothing. It won't go into Fastboot mode or Flash Mode.
There will be white-purplish LED action when I press Power + Vol-Up. First a single blink, three in a row when I hold it for a few seconds. I won't get a red light when not on USB.
That's all. I had the XTZ charged over night (with red LED on) but that didn't change a thing. This is the first time ever bending an Android to my will went sour and I have done it with dozens. Does anyone have any idea what to do?