Disk not recognized after BIOS reset

Hi,

I'm blind and I was having someone fiddle with the BIOS settings on a 
Precision Tower 5810 with a 2Tb SATA hard drive. I thought we'd messed 
things up so I asked her just to restore the BIOS defaults. When sche 
did that, it gave some warning about it possibly making my system 
unbootable but I didn't believe it. But it did because now it doesn't 
recognize the hard drive. Can anyone give me a hint as to what I have to 
tell her to look for to undo this?

I am rather surprised that setting the BIOS back to the defaults causes 
it to not recognise that there's a hard drive in the machine.