I think Chalenge is on the right track. I've never heard that a motherboard would definitely need an SSD for a boot drive. I've been in the belief that at stage the system doesn't actually care about the media as long as it's bootable. Similarly to optical drives, in the boot order list they've been described as CD drives.
Then again, I've often seen the boot device order being far from optimal. If you have USB prior to HDD, then your system will try to boot from any USB disk you have connected, stick and drive equally. Check your BIOS/UEFI boot settings and set the hard disk as the primary one.
For those who have several internal hard drives, setting HDD as primary may not be enough. There's often another screen for managing the hard disk order.
