Periodically, when you turn on the computer, instead of loading the OS, a black screen. What could be?

Question

Windows

There are 2 screws, on both Windows 10, I turn on the computer - a window appears with the choice of OS, turn off the computer, turn it on again - a black screen appears with the _ symbol in the upper left corner. What could it be. In the Boot section, there is only one screw per boot. What could it be ?
UPD I forgot to add right away - in the BIOS in the downloads there is Windows Boot Manager as a bootloader, if you remove it at all, the OS does not load.
It is written like this Windows Boot Manager (screw name)

Answer 1

After all, your disk is marked in GPT, and UEFI is enabled, right? It's because of tricks like yours that I don't like UEFI and GPT, and I suggest others not to like it. In MBR, everything is much more transparent.
Try to fix the problem by switching from GPT partitioning to MBR partitioning. Everything is done by booting from one of the popular LiveDVD / LiveUSD, using the 2k10 repair and recovery package (I personally use the MultiBoot build ).
First, convert GPT->MBR (with Paragon HDM). Then demolish a bunch of miniature system partitions, leaving C and D (the second one is for storing user data), attach the empty space to the nearest large ones. Turn off UEFI in BIOS (i.e. turn on CSM). And finally, restore the boot with the BootICE utility, choosing the latest bootloader type (lowest in the list). There are many download restorers in the 2k10 package, one will not help - try the next one, and to the bitter end (I didn’t succeed right away either).