The difference between data loss and data corruption depends on your checkbook because usually data corruption is going to be written off his data loss. I say usually because there are instances where running something as simple as like a Check Disk type operation may win stuff back or doing some NTFS recovery type tools. There's a lot of third-party programs that are out there that can do some scan and fix type operations and those tools usually take a long time.
They can sometimes get back most of your stuff that's kind of an all-or-nothing gig usually and very few of them cost more than a couple hundred bucks. So that's a really good first line to deal with data corruption. If those tools don't work though, you can sometimes recover that data. You have to send it off to some pretty high-end folks and that's where the budget comes into play. Once you get past that kind of initial line of self-help. It gets very expensive very quickly and at that point it pretty much becomes data loss.