gPhotoShow is two programs in one. It can work as a screen saver and a slideshow maker. When started as Slideshow Maker its main window has two additional buttons "Save" and "Load". These buttons allows you to save/load settings from files on disk but these files are not used by the screen saver. Screen saver has its own settings. The Slideshow Maker always starts with default settings (and empty folders list) while the screen saver always load its settings.
This is gPhotoShow when started as Screen Saver:
This is gPhotoShow when started as Slideshow Maker:
In the start Menu you can find different shortcuts for the Slideshow Maker and the Screen Saver:
By design Windows 10 doesn't start the screen saver when pc is locked. Windows 10 Lock screen has its own settings to display pictures.
What I can suggest is to run the ControlSS utility installed by gPhotoShow and configure hot corners or a hotkey to start screen saver, in this way instead of locking the pc you can manually start the screen saver. If windows is configured correctly, when screen saver is stopped by moving mouse or pressing a key pc will be locked.
If the screen saver works from the preview but doesn't start when computer is idle usually the problem is due to windows. On windows no screen saver starts by itself, idle detection is performed by windows then when it decides the system was idle enough it starts the configured screen saver. There are some things that makes the situation more complicated, some programs (for example media players) disable the screen saver when they are running and windows itself disables the screen saver for some time if you interrupt the screen saver few seconds after it started.
The first thing to try is to open the windows display applet, choose another screen saver wait for it to start then set again gPhotoShow. Usually this fixes the issue until the next time it happens.
If no screen saver starts then probably there is a program that prevent the computer from automatically powering off the display or entering a low-power sleep mode.
It is possible to diagnose this issue using windows powercfg command, open an elevated command prompt then in the command window type:
this command will display all program and devices that prevent the computer from automatically powering off the display or entering a low-power sleep mode. See powercfg help for more info
On windows screen savers never start by themselves. It is Windows itself who detects when the system is idle for the specified amount of time and starts the configured screen saver so this is basically a windows issue. There are several possible causes for this behaviour, some wireless mouses and keyboards prevent the system from being idle so when they are connected the screen saver never starts. Windows Vista and 7 disable the screen saver for some time when it is interrupted within few seconds. Other programs may disable the screen saver as well, for example media players or CD/DVD burning programs often do it for obvious reasons. You could run the ControlSS utility installed by gPhotoShow, it display the screen saver status with an icon in the tray bar so you can see when it gets disabled and enable it again with the ControlSS menu.
gPhotoShow displays a black screen ast startup while it is building the files list or when it can't load any file. The first thing to do is to check the folders you entered in the gPhotoShow folders list, for example make sure they contain at list some images with jpg file extension, then click on the "View Files " button, gPhotoShow will scan the configured folders and will display the files it has found.
If your folders are located on a slow device (USB or network) and you have a huge number of files it is possible gPhotoShow takes several minutes to scan all folders, during this time the screen stays black. To improve startup time enable the option "Background files list synchronization" in the "Files Options" section, when it is enabled gPhotoShow uses a files list saved locally and after the first run it will start within few seconds
The behaviour you noticed is caused by Windows itself, Microsoft decided to disable the screen saver for some time when it is interrupted within few seconds and ControlSS is simply showing you what is happening. Also other programs may disable the screen saver, for example media players or CD/DVD burning programs often do it for obvious reasons.
ControlSS never disable or enable the screen saver by itself, it simply displays the screen saver activation flag.