Hi all. I have a Macbook Pro with a dead display that I am trying to sell in a buy-back program. I connected it via HDMI to my TV to back up all data and then reformat. Immediately afterwards, the HDMI connection stopped working, and so I can't tell if the computer is no longer booting or whether the computer simply doesn't realize it needs to use an external display now that it has been essentially factory reset. I've tried resetting the PRAM, SMC, etc., to no avail. I hear the boot sound but, again, don't know if it's on. Can anyone help to either (a) get the HDMI external display to work again or (b) help confirm that the computer still boots? Thanks!