My Dad's been running with a Grub4dos boot menu dual-booting between Windows 8.1 and Windows 10 for years but he's just let Windows 8.1 update and now there's no sign of the boot menu and it boots straight to Windows 8.1.
I ran BootIce to check and it showed that the Grub4dos MBR was still installed, so it doesn't appear that the Windows updates replaced that. I reinstalled it anyway but it still just boots straight to the Windows 8.1 boot screen.
The only Windows Update that I can imagine might replace the MBR is the Windows Malicious Software Removal Tool, which I always deselect when I'm updating my system. It doesn't appear to have replaced the MBR but maybe it deleted grldr, I haven't checked that yet. Has anyone found that it does that?
That's not the only problem that's started since he did the Windows updates He said after doing them it took ages to shut down and now it seems to get stuck on the Welcome screen doing nothing, as I monitored it for about 10 minutes via TeamViewer and when I opened Task Manager it showed it as 97-99% idle, with nothing under Processes but a load of stuff running under the Details tab.
He also couldn't get into the BIOS, despite power cycling several times and pressing Delete repeatedly. I have the same motherboard (Asus Z97-A) and I see the initial BIOS text and then Delete gets me into the BIOS no problem but my Dad says his monitor doesn't show anything or even any sign that it's receiving a signal prior to the Windows 8.1 Welcome screen appearing and when he presses Delete the monitor never shows anything, so it stops Windows 8.1 booting but doesn't show the BIOS. We're both using graphics cards, (him AMD, me Nvidia) so it's not that the BIOS only appears on a monitor connected to the onboard Intel GPU. I'll have to check what connection he's using though, as maybe he's using DisplayPort and it only displays via HDMI/DVI.
The only thing I could suggest is that he disconnects all his drives other than the boot SSD and if that doesn't work, reset the BIOS by removing the battery but I wonder if anyone has any other ideas about what might be preventing grub4dos working?