System says "No hard disk detected" but boots fine of the SSD

SSDs are more like RAM or thumb drives than they are like regular hard drives.

It is trying to tell you that it can't find your regular hard drive.

Can you use files on it when you are in Windows just fine?

It really depends on your BIOS what you can do to address this issue.

Some BIOSs let you skip certain steps and others not.

Generally speaking, Windows likes to see an attached hard drive, so you may have quite some difficulty trying to get rid of this error.

I'm going to take a different guess; I get a similar message. The motherboard has a Marvell disk controller in addition to the southbridge ports. When I boot without any drives attached to the Marvell controller, and the controller is enabled, I get a similar message. My board is an earlier Asus model.

Look in the BIOS for on-board components and disable the Marvell controller. If that makes the message go away, you can consider leaving it disabled until you need it.

If it can't be disabled in the BIOS and you are really, really curious, disconnect your HDD and connect it to the Marvell-controlled ports. If the message goes away, I was right.

I'd check your boot priorities in your bios and make sure that the ssd is selected as your primary (master) drive. It sounds like it is checking your other drive first and reads that it doesn't have an operating system on it and then checking the next drive and sees that that has windows on it and then boots.