New
#11
Do you have a USB card reader? Sometimes if you have a USB card reader with a memory card inserted, the BIOS will try to boot it and, on my system anyway, this intermittently would KO the SATA interface and the machine wouldn't boot. If it sounds like it could be that, disable USB device booting in the BIOS.
...or, just don't insert a memory card until after you've booted up.