A. This is usually due to an error in the boot.ini file. The entry for NT is either missing or incorrect. Edit the boot.ini file and check the entry for NT is correct, for example for an IDE disk the entry should look something like
multi(0)disk(0)rdisk(0)partition(2)\winnt="Windows NT workstation"
Check that disk and partition are correct. If you have recently added a new disk or altered the partitions try changing the disk() and partition() values. If you are sure everything is OK, then the actual file may be corrupt so copy NTOSKRNL.EXE off of the installation CD onto the %systemroot%/system32 directory.
You may need to edit the boot.ini if Linux is installed onto a system. During installation DiskDruid (Red Hats disk configuration utility) may create a primary partition (depending on disk configuration) and although the extended NT partition was there first (and at the beginning of the disk), the primary partition affects the numbering of the partition() parameter of boot.ini. Changing it from (1) to (2) (for example) allows the successful boot of NT.