Sometime a fresh install of XAMPP has worked to fix these strange errors, by removing the old xampp folder but first you must make sure to stop all xampp components and uninstall any services or you will get errors when you install again.
Reboot before installing again.
Try another version of XAMPP not the installer version this time - the EXE (7zip) version is self extracting and if you select D:\ to extract all the files to it will create D:\xampp and place all the files correctly then you simply run the setup_xampp.bat file in the D:\xampp folder to set all the paths.
Next try all your addresses again and they should work perfectly this time.
When you install to a folder with a space in the name like Program Files, it can give unpredictable results.
These Google search results
will show you just how common and how many different solutions there are for your error "#1130 - Host 'localhost' is not allowed to connect to this MySQL server" including, as I suggest, a fresh install.