BSOD on boot: INACCESSIBLE_BOOT_DEVICE

I run Win10 64bit on an AS-Rock Q1900-ITX board as a PVR backend and connect to it via VNC as and when required for maintenance. The system runs largely trouble free. Recently I rebooted and noticed it had not come back up. Connected to a TV I now see it enters a boot loop with the message above.

Win10 is installed on a 64GB NTFS SSD. It has 3 partitions - System Reserved (350MB), Windows (55GB) and 1 other at 450MB. There is also a 3TB HDD for data (NTFS, single partition)

I have looked around this board and the internet for solutions and put it down to EFI/MBR issues. I have seen an error message at times stating an issue with \EFI\Boot or similar. I am pretty handy with IT but this problem has had me stumped for a week. I have tried the Windows recovery disk USB created on another machine (which fails to fix) and various 3rd party ones along with Linux live disks etc which all work and the disks in the system are intact and functioning normally but I feel I am getting further away from a solution to getting it booting again.

Unfortunately I cannot run the diagnostic tool as mentioned in the thread stickies.

Any help greatly appreciated before I have to re-install which I am reluctant to do due to the amount of config necessary for TV channels etc.

Thanks.

Thanks for that. I'd had a further play last night and made things worse so decided to re-install to save any more messing.

After the re-install I can now see the drive has been partitioned differently with a 100MB EFI partition which wasn't there before. This legacy/BIOS/GPT stuff is really beyond me.

I am now booting to Windows again, however, a restart in Windows causes the PC to hang on the POST screen when booting with "9C" in the corner. A power cycle reboots to UEFI settings and finally, a "save and exit" there boots to Windows properly. Without a screen I really need to be able to hit "restart" and assume that the machine will do just that.

Any thoughts?