NT syas DAMAGED partition

I have Cyrix 500 MHz Mercury EFSt M/b with 20GB HDD with 7 partitons 2GBx4 and 4GBx3. First OS is WIN98. When I try installing WINNT Server, it shows three partiton and all damaged. When I try installing WIN2K server, it denied to change partion to NTFS (FAT16). But installation was successful on FAT16 as second OS (Dual Booting). Now DISK MANAGER showing all partitions as healthy. Any clue. Thanx in advance