Failed to open \EFI\BOOT\grubx64.efi

[andrewj720]

I have been running CentOS 7, for around 1 year, on a laptop, with few issues.

Yesterday I removed the SSD from the laptop, inserted an HDD (to RTZ it), and this morning, put the SSD with CentOS on it back in the laptop.

I was unable to boot in. I got the following error messages:

Failed to open \EFI\BOOT\grubx64.efi - Not Found
Failed to load image \EFI\BOOT\grubx64.efi: Not Found
Start_image () returned not found

All the solutions to repair the boot process, but all the ones I've found refer to booting a repair disk, but when I try this from a CentOS 7 .iso on USB, I get error messages:

error: /images/pxeboot/vmlinuz has invalid signature
error: you need to load the kernel first.

Does anyone know how I can repair my CentOS 7 installation?