No one who assembles a PC or sets up a new computer can avoid the BIOS or UEFI. That’s where you define the basics, from the boot sequence and memory profiles to security features like Secure Boot.

Its probably just the boot order. Go into the BIOS and make sure its trying to boot from the correct hard drive first. If you aren't sure what drive you are supposed to boot from, just switch whatever ...

If there are multiple drives installed in the computer, then it can create confusion as to which drive has a Bootloader. This scenario usually happens when Master Boot Record is on the wrong drive.