ThingWorx 8.4 F000 is six years old, you really shouldn't use it anymore. You won't find much help for such an ancient system, because no one is able to test it anymore.
Still, you should check what error messages you have in ApplicationLog immediately before you see that "xxx not running" error -- this will give you some idea of what causes it.
Hi @SZ_8739263
Did you check the Application log for the cause of the issue? You can find this log under ThingworxStorage\logs unless the default path was changed at the time of installation.
One possible cause of the problem is license expiration. Even if you're running an older release, you can still get an updated license, though I agree with Constantine, that it would be best to upgrade. There have been numerous security and functional changes in the current versions.
Please let us know how we can help.
Regards.