Hi Sam;
I have never seen the Target Wizard dialogue box empty like this in all my years using PB. I suspect that its related to either an improper PB installation, running on old version of PB on an unsupported version of MS-Windows or a Windows resourcing issue.
May I suggest:
1) If you are on a newer MS-Window release - Try running your PB IDE in ADMIN mode and/or in "Compatibility" mode
- if #1 does not work ....
2) Try uninstalling & then reinstalling PB. Also make sure that you also install any Maintenance Releases related to that PB version.
Good luck!
Regards .. Chris