Thanks for getting back to me. After posting the question I eventually remembered what I did the last time to fix it. I'll post the solution here just in case someone else has the same problem.
I went to my PD16 folder and found the execute file
I right clicked on it, and went Properties
I went to Compatability and selected run this program in compatability mode for Window 7
I also ticked run this program as administrator
I saved everything and, right clicking the execute folder again, I created a PD16 shortcut onto my desktop
That shortcut has all the changes I made, and PD16 ran fine after that. Hope this helps.