|"ntldr is missing"|
It is RARE that this is hard drive related.
Most common reason for this is virus/malware infection or a drive that has never been defragmented.
Having one drive for OS and the second drive for DATA is an OPTIMAL [very best] configuration. Don't change it.
Your first step would be to boot into Recovery Console and run chkdsk /r on the master drive. This will make sure you don't have file level/disk level corruption.
Next step would be to do a repair install of xp. This is not a reinstall like from scratch but a install to repair xp system and boot files.