New Motherboard - Boot Disk Error

I am putting a new motherboard, processor and Memory in my sisters computer. When complete putting it together and start it up, it reads the memory and then throws a "Boot Disk Erorr, insert Boot disk and hit enter" I plugged the hard drive into my pc and it works fine, plugged my hard drive into this machine same thing. Unplugged everything except the harddrive same thing.
Originally thought it was the IDE drive on the motherboard or cable, replaced cable samething, received new motherboard same thing..

Can't figure out what I am missing.
Any help would be great.

The new motherboard is ASUS - A7S8X-MX
DDR Ram
AMD Sempron 3000+ Socket A CPU

 

Check the BIOS and make sure IDE0 is the first boot device and not the CD, A drive, or something else.

 

And make sure you've got the IDE cable plugged in the right way round which can happen if the plug does not have a cutout or guide.

 

Thank you I will check the BIOS I have once before but I will verify...
I went home over lunch and now the thing won't even turn on. Will have to look it over again tonight.