If you have a hard drive on an IDE cable all by itself, its set as a single.
Now if you hook it back up and switch the cables, you will not see the drive.
A drive set up as a Master on an unshared IDE will not be seen. A drive set up as a single on a shared IDE may or may not be seen depending on how the cdrom is configured
If you have an IDE cable with a small square hole punched in it--this is a "cable select" cable (Compact and Dell use them). In that case the middle connector goes to the hard drive. It won't boot from the end one.
It is also possible to have the cable in the hard drive socket or the motherboard the wrong way
Hope this helps get you out of the "doghouse"
