There is nothing wrong with the hard drive.
This is happening because Windows does not recognize or support the file system utilized by Linux. Sometimes Windows sees it, sometimes it doesn't. I personally don't know the cause of that. Just because it's listed as RAW doesn't mean there's anything wrong with it really. RAW explained on Microsoft's TechNet:
"It's simply a disk partition that has not been formatted with an NT file system, neither FAT nor NTFS."
If you can still boot to Ubuntu fine, there is nothing wrong with the partition. Some partition programs, like Partition Magic, will recognize the partition from within Windows and will show what it is correctly, but it still won't be accessible.
Oh, and I wouldn't try repairing it as Dusty suggested. Considering Windows can't actually read the Linux partition, it might damage it trying to "fix" it.
