I can open DPro in SPlat but, when loading a preset, get a message that the samples can't be found. Should I re-install DPro or this there another solution? It was working OK but I think my external HD's (where I initially installed D-Pro) may have remapped themselves with a different drive letter. 

You do not need to reinstall. DPro reads the path to the samples from Multisamples Folder in the registry
HKEY_LOCAL_MACHINE\SOFTWARE\Cakewalk Music Software\dp
 
You can fix the problem by updating the registry or changing the drive letter back to what it was using (Google "change drive letter windows 10" for instruction")

If the paths are okay, try this (from CW Knowledge Base):
 
Press F5 with focus on the Program Browser, this will automatically update and refresh the Program list.

F5 will not fix missing sample problems. F5 rebuilds the programs.lst the file used to construct the contents of the DPro browser. This file is located in C:\ProgramData\Cakewalk\Dimension Pro and it contains the .prog files found in C:\ProgramData\Cakewalk\Dimension Pro\Programs. The process has nothing to do with sample locations.

Thank you for your advice. I will give that a run and see how I fare.

Thanks again. Edited the registry and all back to normal.