hold power for 10+ seconds until the soft keys start to blink. this will initiate a hard reset. when the phone turns off to reboot,start holding vol down. this should get you to hboot. select recovery,and see if you can get to recovery. if so,you can restore a backup or flash a rom.
if you need to,you can repeat that process,then when you get to bootloader,select fastboot. plug in,and you should get a serial number from fastboot devices
you can now reinstall a recovery. let the phone try and reboot after installing,repeat the hard reset/hboot/recovery process to get into a working recovery.
install a rom or restore a backup. hope that helps