For some people there are unexplainable and unsolvable issues with using the installer version of XAMPP on some Windows version that is best solved by starting again with a clean uninstall and then using the zip version
not the installer exe version of XAMPP.
So try this by uninstall this instance using the instruction in the readme_en.txt file in the xampp folder...
...when you have stopped all XAMPP components and removed any ticks in the Svc check boxes in the XAMPP Control Panel then you can EXIT the Control Panel and delete the xampp folder.
Now download the zip version of XAMPP and extract the xampp folder to the C:\ drive so you end up with C:\xampp
Now run the setup-xampp.bat file which will do some work then ask you to close it.
Next double click on the xampp-control.exe file and start Apache and MySQL only.
Now go to http://localhost
and select your language and then see if you can do all the demos.
Let me know if by following the above instructions you still have problems.
BTW clear you browser's temporary file cache and do it often.