Something else to try:
In the Windows Services window look for "JRiver Media Center 32 Service".
In its Start Type column, be sure the setting is "Manual" (not "Automatic").
To change it: RMB on the entry > Properties > Start type (in popup) > Manual
If that does not help, you can try selecting "Disable", but I'm not sure where that will leave you in terms of MC performance, and it shouldn't be necessary anyway.
While you are there, if old versions are listed, either delete them or set to "Disable".
Some ways to find the Windows Services window:
1) Windows Taskbar search box, enter "Services". Run as administrator.
2) RMB Windows Taskbar > Task Manager > Services Tab > RMB Media Center 32 > Open Services.
BTW, re registry: I recently used regedit to search my registry for "media". I must have found well over 50 entries referring to old uninstalled versions of MC, going back to version 28 right up to MC 31 and 32. I took a chance and very carefully deleted every entry prior to MC 31. So far, no ill effects noticeable. That kind of extensive registry cleanup should not be necessary, and I don't recommend messing with the registry directly to solve your problem.