Did you install any applications at all after flashing the various ROMs? That type of problem screams "installed cab issue", particularly if the screen does
eventually turn on (which to me rules out a hardware problem). Do you have anything installed on a memory card, and/or a really slow (or huge) memory card in place? What happens when you flash the stock ROM, install nothing, and don't use a MicroSD card?
As for returning,
AFAIK you'd flash back to stock and relock. Instructions are in various places around here (I suspect there might even be a sticky).