My "C" drive (a SATA drive) shows everywhere except in Disk Management. All other drives (DVD and 2 SATA storage drives) show in Disk Management. What can be the cause?
I take it that the C drive shows up in My Computer, but not in Disk Management? In that case it's probably not a HDD problem. Instead, those symptoms point to the TDSS rootkit. It can often go unnoticed for weeks or even months since it is somewhat hard to detect. I had the EXACT same symptoms when I had the TDSS rootkit: C drive no longer in disk management, other drives no problem. Took me over a month to find and remove it.
You can follow the procedure in the link below to detect/remove the TDSS rootkit:
Make sure that both "Services and drivers" and "Boot sectors" are checked (TDSS often resides in the boot sector).
If the rootkit is removed properly and the machine rebooted, the C drive should reappear in disk management.