No, but then nothing can up saying to activate this

Minimize all windows and see if you can find the activation box, and enter the registration code. Might be the anti-piracy function that kicked in.

I've searched my computer and cannot find any activation boxes

It should come up when you select the PMDG 737 aircaft inside P3D. Sometimes the activation box hides behind the P3D window. If you can't find it try and submit a ticket at http://support.precisionmanuals.com/

I'll submit a ticket

Haha..did you install the sim connect libraries in p3d as mentioned in the manuals or release notes in your pmdg setup..if u dont see activation box then probably that is the reason

I installed the simconnect from the redist folder in P3d - which I did last time I installed P3D