Not showing startup menu after dual booting

[Alex1386]

I have an HP EliteBook 850 G5; it has preinstalled Windows 11. I wanted to dual boot it with Linux (Garuda Mokka), and I installed it successfully by disabling secure boot. The laptop showed me two OS options, and then I went to the login page of Linux. From there, I restarted the laptop. Now the thing is that the screen shows the HP logo, then blanks out, and then the logo shows again and blanks out. I tried to go into the startup menu and boot settings, but nothing happens. All the function keys are working properly. I also used the 30-second power drain method and the Windows + B method, but nothing works. The laptop is in a loop.

[TheOldMan]

It would seem the boot loader is corrupt.  Linux usually uses Grub to make the new boot loader.  So a repair of the new boot loader needs to be accomplished.  It will require booting the PC to either the Linux install media or the Windows install media and then repairing the boot loader.  Repair of the boot loader can be done from a command line, but letting Windows install media or Linux install media is simpler.  The install media for Garuda Mokka includes the ability to load the "Live" version, so go there to use Grub to repair the boot loader or use the Windows install media and the "Repair this PC" or whatever it is called on the Windows 11 install media.