I just installed 8 and fully updated it. I was using an external CDROM and so I installed AcetoneISO for the install media to be present without the CDROM. Upon starting up the next day, GRUB can't find the boot disk.
Here is the thing...I go into BIOS and exit. My m.2 is the only boot device. It boots right up. I reran the boot loading from the Controls and that does not fix it. If I unplug my SATA 3T data drive, it boots right up. Going to attempt that again after I put the SATA to hotplug. Yes, it boots right up without the 3T drive powered.
I ran Win10 bootrec and it can't get rid of GRUB but it boots properly the FIRST time after the Windows bootrec session. Then it reverts to not being able to see the boot disk until after the BIOS.
Rather annoying....