I installed Lotus Notes 8.5 Basic as a PortableApp following the directions posted on this site (thank you very much). When Notes-as-PortableApp runs, it makes several changes in the Registry which are removed upon exit. Generally, that works very well. If you experience a hang, however, it will not remove those entries. And, it will not remove them when you run it thereafter.
If you have Lotus Notes installed on the machine (Notes 8.5.2 Standard on Windows 7 in my case), you will still be able to run the machine-based Notes, but will end up with hard-to-diagnose problems. In my case, it broke the mailto URL settings among others. Specifically, programs which rely upon that setting failed with a message that no default email program is configured.
In my case, the hang occurred so long ago that a system restore was not possible. The solution I used was to search the Registry for a portion of the Portable App directory, which I then replaced with the proper directory for the machine-based Notes.