Have you tried to install QVS twice on the same domain with the same non-clustered license? Is the service account under which the QV services are running (a) a local admin? (b) a QlikView Admin? (c) authorized to logon as a service?
Under Status --> Services, make sure the QVS service is green or else things will start to fail. A good first step is to restart the service. If that doesn't fix it, check the settings above.