Hi
Make, Model and OS please.
SKU: if possible
(System SKU: N6K07EA#ABU)
Please do not post Serial Numbers.
If you installed as a secure boot OS then Grub should just work.
If you installed as Legacy, and the BIOS is looking for a Secure Boot option then....
3F0 usually means a failed HDD, so ESC and F2 diagnostic.
ELSE
Look at the BIOS options for LEGACY/SECURE and selection of BOOT MANAGER.

