I have a similar problem like this previous post.
So, I am using ASUS motherboard desktop. Previously the OS was Windows 10, very probably in UEFI mode, I did not check that, and that was my worst mistake. Recently I installed Ubuntu 22.04 LTS on it as dual boot. The Ubuntu I installed in Lagacy/BIOS mode. After that, I could see both Windows and Ubuntu from the GRUB menu, but only Ubuntu could load, and Windows 10 was not loading (just black screen). I found out that this is because of the two separate modes of these two OSs.
As I could not open Windows 10, I thought it could be a good idea if I changed Ubuntu to UEFI mode. I tried a few google suggestions, finally I tried with BOOT_REPAIR:
- In advanced mode, very probably I select the MBR Disk partitioning and reboot the computer.
However, after that reboot, I now even cannot see the grub menu. It is just a black screen and in the top left corner the cursor blinking. I tried pressing shift or esc key for some time to bring back the grub menu, but it did not work.
Also tried to change menu BOOT>> CSM enable/disable, Secure boot enable/disable. It did not work. Moreover, disabling CSM is just reloading the BOOT menu each time I reboot the computer.
The final option I may try to re-install Ubuntu in UEFI mode, but I cannot lose any of these Operating systems at this moment because of the software-configuration and files.
Any suggestion ?
