Try booting into recovery and flashing your backup ROM. (You did make a backup, right?). Then go into ROM manager and flash the alternate recovery at the bottom. Then go back into clockwock and flash ClockworkMod Recovery. Then try flashing your ROM again. You said you flashed FROYO, which one? You might have flashed a theme, (which goes over a ROM). If this is the case, you need to flash a full ROM, then a theme. Hope this helps.