See e.g.
Wikipedia on chkdsk. As someone has pointed out, RAID is not a supported technology for Windows Home Server. There's
a post on the WHS team blog giving some reasons why.
As for your specific issue: it's likely that a failure of some sort occurred (maybe the RAID controller, maybe the RAID driver, maybe some other system or driver related to the file system). It's hard to say at a distance. You could try booting from a Linux live distro that includes an NTFS driver to see if the array is still readable. If it's not, you can consult with the manufacturer of the RAID controller to see if there are recovery tools or techniques available. But there's a pretty high likelihood that you've lost any data stored only on that array, I'm afraid.
I'm not on the WHS team, I just post a lot. :)