I had just gotten Sierra working. I went to bed and left the machine to sleep. Woke up this morning to wake my Hack, and it wouldn't wake. The fans came on, but the displays wouldn't. So instead of moving the mouse or hitting a key on the keyboard I tried tapping (not holding) the power button. The machine switched off. Normally if I just tap the power button, it would only switch off if I was in BIOS or the Clover bootloader menu, or during startup. Anyway, I tried turning it on again, and the machine starts up, except the displays don't. So I don't even know if the BIOS is coming up. Have tried taking out the battery from the motherboard and putting it back in again, removing and putting back again the graphics card, the ram... even the SSDs. I've tried jst using one screen plugged into the motherboard's DVI port.... still nothing. Holding down the power button will switch it off (tapping it won't).