Thanks for the info notladstyle.
It looks like the original poster has given up, or hopefully figured it out.
fanoush's terminal commands probably are as thourough as you need, but there is a 'last resort' test you could perform. You can format the card with the back cover off (it has to be unmounted). You could try sfdisk /dev/mmcblk0 -uM and then just cancel out if you don't want to format it. That would confirm the card is accessable at some level.

For what it's worth, I had trouble booting off of the internal card. It wouldn't be detected at startup, but was still able to be mounted and used for data file storage. This turned out to be helpfull since the internal is the first one mounted by windows, and my work PC only had one slot that wasn't mapped. The problem went away, I don't know how though.