You might be able to use the information to determine if a device's Location Services are active or not by polling these LocationSensor Properties:
Enabled If true , the LocationSensor will attempt to read location information from GPS, WiFi location, or other means available on the device. This setting does not control whether location information is actually available. Device location must be enabled or disabled in the device settings.
AvailableProviders List of available service providers, such as gps or network. This information is provided as a list and in text form.
ProviderName The current service provider. The provider will most likely be either GPS or network.
ProviderLocked The device will not change the service provider. It is possible for a device to switch service providers when the current provider is unable to provide adequate location information. ProviderLocked is a Boolean value: true/false. Set to true to prevent providers from changing. Set to false to allow for automatic switching when necessary.
See the full discussion in the LocationSensor documentation.
Be aware it is impossible to turn on or turn off Location using Blocks. Setting Location Services must be done using the Settings on your device. See Gps enabled / disabled, but does it work?
What you do depends on why you need to change Screen if the GPS hardware is disabled. What have you tried? You might try this example Problema initializar latitud y longitud gps al momento de inicializar pantalla