Before trying the following procedure, make sure your BIOS settings reflect the mode (LBA, Normal, Large) in effect when the disk was originally partitioned and was operating normally.
If the settings are the same or the disk is still inaccessible after changing the settings, then continue with this last-ditch-effort.
This is a destructive procedure -- it will overwrite the partition table and master boot record. The data will not be modified. However, if the procedure does not re-enable access to the drive, the original partition information (which appears now to be corrupt) will definitely be lost.
There is an option in PART.EXE (see below) that will allow you to save the original partition table and master boot record to a diskette.
Download this file and unzip it. Create a DOS boot diskette and put the expanded files on it. Boot the machine with the goofy disk using the boot diskette.
Run PART.EXE and manually remove all the partitions and re-create an NTFS partition that spans the entire drive. Save the changes and reboot NT.
http://www.users.intercom.com/~ranish/part/part.zip