What ATAPI stands for I can't expand. It doesn't really matter anyway and Google will tell you what it stands for .........but the error message is telling you that you can't boot from your CDROM, either there isn't a suitable disk in the drive, or the drive has failed in some way.
In your mobo BIOS there should be options for First Second and Other boot device.
I usually set Floppy as first device and HD 0 (that is zero) as the second.
My computer then quickly notes that there is no floppy in Drive A: and promptly looks for the boot drive on the first HDD that is C: or HD number zero.