Take a look at your boot priority, you'll either see the name of the drive your OS is installed on (ie WD Blue 1TB), or you'll see "Windows Boot Manager".
Ensure that's set to priority #1 (select "boot manager" if it's present)
What is set to boot priorty #1 in the BIOS? If it has somehow retained the boot priority for a drive that's no longer attached (or you have no OS installed) there's nothing to boot to - therefore, it'll boot into the BIOS.
Take a look at your boot priority, you'll either see the name of the drive your OS is installed on (ie WD Blue 1TB), or you'll see "Windows Boot Manager".
Ensure that's set to priority #1 (select "boot manager" if it's present)