If it doesn't even show in Disk Management, it seems it have gone south. Can happen. And it's a good explanation of the program failing.
Things you can do to doublecheck that diagnosis:
1. Boot into a Linux Live CD and see what that says
2. Get it out and into an external enclosure, then try on another PC.
3. Get it out and try it on another PC as an internal disk
If no luck, buy a new disk and restore your files from your latest backup.