NTFS partition recognised by everything but Windows

Recently, a Windows XP machine got into the "UNMOUNTABLE_BOOT_VOLUME," endless-reboot loop, so I tried the usual things, such as CHKDSK /P /R, FIXBOOT, and FIXMBR. When none of those worked, I tried a number of other tools, ranging from KNOPPIX to the HIRENS Boot Disk.

The difficulty is this: under anything that is Windows based, the drive shows as an "unknown" partition type, and it says that no space is allocated, and that the entire partition is free. CHKDSK, however DOES report accurate information, even though DIR will not work at all.

Under KNOPPIX, or the like, the partition shows up as type 7 (NTFS), the free space is correctly reported at 43%, and all the files are accessible (in fact, I copied the whole lot to a shared drive on another machine, just in case).

Even if I use fdisk under KNOPPIX to "change" the partition type to 7, rewrite it, then reboot, Windows still considers it "unknown," and gives the "UNMOUNTABLE_BOOT_VOLUME" BSOD.

If EVERYTHING were gone, I could understand just going ahead with a fresh installation of Windows, but since everything BUT Windows is able to use the drive and partition with no problems, it would seem there must be SOME way for some tool to set things aright for Windows.

I have already checked similar questions and discussions here and on other sites, and although I certainly cannot claim to have been 100% thorough, I can honestly say that I have already tried ALL of the suggestions in the dozen or so that I HAVE checked - one way or another, still leaving me with the conditions stated above.

Any further ideas?

Thanks!