This is a strange and unnerving issue.
Several people (about 5 at last count) have reported on the MyDellMini forum
that their Mini's SSD became unusable (shows as 0MB capacity in BIOS) after doing an install or upgrade of Windows 7. While I have done several installs and upgrades of Windows 7 on my Mini 9 without issue, I did have this exact problem with a WD "Caviar Green" 1TB drive on my desktop.
The way it worked for me was that I upgraded from 7000 to 7100. The upgrade itself seemed to work fine, but the next time I rebooted, the BIOS showed 0MB capacity on the HDD. I took this drive to three other systems and none of them could get at the drive. The WD diagnostics recognized that there was a WD drive there, but then reported a fatal error.
If this had just been me, I would have chalked it up to a bad drive (which WD is replacing). But to have multiple people report the same problem, and not all using the same brand of SSD, tells me that something real is going on here. I have searched this forum and elsewhere and not found reports of this problem - has anyone here seen the issue or seen it reported elsewhere? I don't know what to do next - it makes me afraid of doing further installs of Windows 7, though it hasn't stopped me yet.